refactor(workspace): migrate from per-folder windows to single-window workspace

Replace the legacy folder + welcome routes with a unified /workspace route
that hosts all folders, conversations, tabs, and terminals in one window.

- Persist opened tabs to the database (opened_tabs entity + migration)
  so tab layout survives restarts and deep-link bootstrap restores state
- Replace FolderContext shim with AppWorkspaceProvider, ActiveFolderProvider,
  and TabProvider; expose both opened (folders) and full DB (allFolders)
  listings via list_all_folder_details
- Return conversations across all non-deleted folders from list_all when
  no folder filter is given, so the sidebar can show every folder's history
- Add ConversationContextBar above the chat input with folder picker
  (auto-opens unopened folders on select), branch picker, and commit /
  push / merge / stash entries to restore BranchDropdown functionality
- Rework sidebar with stats header, search, flat / folder-grouped view
  modes (localStorage-persisted), reveal-in-sidebar event subscriber,
  and per-folder context menu (focus, close tabs, remove from workspace);
  indent conversations under folder headers in grouped mode
- Gate terminal creation on active folder and show folder context
- Remove deprecated BranchDropdown, FolderNameDropdown, welcome route,
  and per-folder window commands
- Localize all new strings across 10 locales

src/components/project-boot/shadcn/create-project-dialog.tsx

@@ -37,7 +37,7 @@ import {
 import { isDesktop, openFileDialog } from "@/lib/platform"
 import {
   createShadcnProject,
-  openFolderWindow,
+  openFolder,
   detectPackageManager,
 } from "@/lib/api"
 import { extractAppCommandError, toErrorMessage } from "@/lib/app-error"
@@ -122,7 +122,7 @@ export function CreateProjectDialog({
       toast.success(t("toasts.createSuccess"))
       onOpenChange(false)
       resetForm()
-      await openFolderWindow(projectPath)
+      await openFolder(projectPath)
     } catch (err) {
       const appErr = extractAppCommandError(err)
       const message =