refactor(branch-dropdown): drop worktree parent-branch merge shortcut

Remove the parent-branch button shown beside the branch selector along
with its supporting API, command, service, model, and i18n strings.
Add migration m20260423 to drop the now-unused folder.parent_branch
column.

src/components/layout/branch-dropdown.tsx

@@ -5,7 +5,6 @@ import {
   ArchiveRestore,
   Archive,
   ArrowDownToLine,
-  ArrowLeftRight,
   ChevronDown,
   ChevronRight,
   FolderGit2,
@@ -77,7 +76,6 @@ import {
   openCommitWindow,
   openPushWindow,
   openStashWindow,
-  setFolderParentBranch,
 } from "@/lib/api"
 import { openFileDialog, subscribe } from "@/lib/platform"
 import { RemoteManageDialog } from "@/components/layout/remote-manage-dialog"
@@ -130,7 +128,6 @@ export function BranchDropdown() {
   const branch = activeFolder
     ? (branches.get(activeFolder.id) ?? activeFolder.git_branch ?? null)
     : null
-  const parentBranch = activeFolder?.parent_branch ?? null
 
   const [branchList, setBranchList] = useState<GitBranchList>({
     local: [],
@@ -349,15 +346,9 @@ export function BranchDropdown() {
     await runGitTask(t("tasks.newWorktree", { name }), async () => {
       await gitWorktreeAdd(folderPath, name, wtPath)
       await openFolder(wtPath)
-      await setFolderParentBranch(wtPath, branch)
     })
   }
 
-  function handleMergeParent() {
-    if (!parentBranch) return
-    setConfirmAction({ type: "merge", branchName: parentBranch })
-  }
-
   async function handleConfirm() {
     if (!confirmAction) return
     const { type, branchName } = confirmAction
@@ -818,18 +809,6 @@ export function BranchDropdown() {
         </DropdownMenuContent>
       </DropdownMenu>
 
-      {parentBranch && (
-        <button
-          className="flex cursor-default select-none items-center gap-1 rounded px-1.5 py-0.5 text-xs text-orange-500 transition-colors hover:bg-accent hover:text-orange-600 dark:text-orange-400 dark:hover:text-orange-300"
-          disabled={loading}
-          onClick={handleMergeParent}
-          title={t("parentBranchHint", { parentBranch })}
-        >
-          <ArrowLeftRight className="h-3 w-3 shrink-0" />
-          <span className="max-w-32 truncate">{parentBranch}</span>
-        </button>
-      )}
-
       <AlertDialog
         open={confirmAction !== null}
         onOpenChange={(open) => {

src/i18n/messages/ar.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "لا توجد فروع محلية",
       "remoteBranches": "الفروع البعيدة ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "لا توجد فروع بعيدة",
-      "parentBranchHint": "تم إنشاء الفرع الحالي من {parentBranch}. انقر لدمج {parentBranch} في الفرع الحالي.",
       "dialogs": {
         "newBranchTitle": "فرع جديد",
         "newBranchDescription": "إنشاء فرع جديد من الفرع الحالي {branch}",

src/i18n/messages/de.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "Keine lokalen Branches",
       "remoteBranches": "Remote-Branches ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "Keine Remote-Branches",
-      "parentBranchHint": "Der aktuelle Branch wurde von {parentBranch} erstellt. Klicken, um {parentBranch} in den aktuellen Branch zu mergen.",
       "dialogs": {
         "newBranchTitle": "Neuer Branch",
         "newBranchDescription": "Neuen Branch vom aktuellen Branch {branch} erstellen",

src/i18n/messages/en.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "No local branches",
       "remoteBranches": "Remote branches ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "No remote branches",
-      "parentBranchHint": "Current branch was created from {parentBranch}. Click to merge {parentBranch} into current branch.",
       "dialogs": {
         "newBranchTitle": "New branch",
         "newBranchDescription": "Create a new branch from current branch {branch}",

src/i18n/messages/es.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "Sin ramas locales",
       "remoteBranches": "Ramas remotas ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "Sin ramas remotas",
-      "parentBranchHint": "La rama actual fue creada desde {parentBranch}. Haz clic para fusionar {parentBranch} en la rama actual.",
       "dialogs": {
         "newBranchTitle": "Nueva rama",
         "newBranchDescription": "Crear una nueva rama desde la rama actual {branch}",

src/i18n/messages/fr.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "Aucune branche locale",
       "remoteBranches": "Branches distantes ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "Aucune branche distante",
-      "parentBranchHint": "La branche actuelle a été créée depuis {parentBranch}. Cliquez pour fusionner {parentBranch} dans la branche actuelle.",
       "dialogs": {
         "newBranchTitle": "Nouvelle branche",
         "newBranchDescription": "Créer une nouvelle branche depuis la branche actuelle {branch}",

src/i18n/messages/ja.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "ローカルブランチはありません",
       "remoteBranches": "リモートブランチ ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "リモートブランチはありません",
-      "parentBranchHint": "現在のブランチは {parentBranch} から作成されました。クリックして {parentBranch} を現在のブランチにマージします。",
       "dialogs": {
         "newBranchTitle": "新規ブランチ",
         "newBranchDescription": "現在のブランチ {branch} から新しいブランチを作成",

src/i18n/messages/ko.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "로컬 브랜치가 없습니다",
       "remoteBranches": "원격 브랜치 ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "원격 브랜치가 없습니다",
-      "parentBranchHint": "현재 브랜치는 {parentBranch}에서 생성되었습니다. 클릭하여 {parentBranch}를 현재 브랜치에 병합하세요.",
       "dialogs": {
         "newBranchTitle": "새 브랜치",
         "newBranchDescription": "현재 브랜치 {branch}에서 새 브랜치를 만듭니다",

src/i18n/messages/pt.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "Sem branches locais",
       "remoteBranches": "Branches remotas ({count, plural, one {#} other {#}})",
       "noRemoteBranches": "Sem branches remotas",
-      "parentBranchHint": "A branch atual foi criada a partir de {parentBranch}. Clique para mesclar {parentBranch} na branch atual.",
       "dialogs": {
         "newBranchTitle": "Nova branch",
         "newBranchDescription": "Criar uma nova branch a partir da branch atual {branch}",

src/i18n/messages/zh-CN.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "无本地分支",
       "remoteBranches": "远程分支 ({count})",
       "noRemoteBranches": "无远程分支",
-      "parentBranchHint": "当前分支从 {parentBranch} 创建，点击合并 {parentBranch} 到当前分支",
       "dialogs": {
         "newBranchTitle": "新建分支",
         "newBranchDescription": "从当前分支 {branch} 创建新分支",

src/i18n/messages/zh-TW.json

@@ -1082,7 +1082,6 @@
       "noLocalBranches": "無本地分支",
       "remoteBranches": "遠端分支 ({count})",
       "noRemoteBranches": "無遠端分支",
-      "parentBranchHint": "目前分支從 {parentBranch} 建立，點擊合併 {parentBranch} 到目前分支",
       "dialogs": {
         "newBranchTitle": "新增分支",
         "newBranchDescription": "從目前分支 {branch} 建立新分支",

src/lib/api.ts

@@ -656,16 +656,6 @@ export async function getFolderConversation(
   return getTransport().call("get_folder_conversation", { conversationId })
 }
 
-export async function setFolderParentBranch(
-  path: string,
-  parentBranch: string | null
-): Promise<void> {
-  return getTransport().call("set_folder_parent_branch", {
-    path,
-    parentBranch,
-  })
-}
-
 export async function removeFolderFromHistory(path: string): Promise<void> {
   return getTransport().call("remove_folder_from_history", { path })
 }

src/lib/tauri.ts

@@ -524,16 +524,6 @@ export async function getFolderConversation(
   return invoke("get_folder_conversation", { conversationId })
 }
 
-export async function setFolderParentBranch(
-  path: string,
-  parentBranch: string | null
-): Promise<void> {
-  return invoke("set_folder_parent_branch", {
-    path,
-    parentBranch,
-  })
-}
-
 export async function removeFolderFromHistory(path: string): Promise<void> {
   return invoke("remove_folder_from_history", { path })
 }

src/lib/types.ts

@@ -160,7 +160,6 @@ export interface FolderDetail {
   name: string
   path: string
   git_branch: string | null
-  parent_branch: string | null
   default_agent_type: AgentType | null
   last_opened_at: string
   sort_order: number