fix(git): surface non-git-repo as a typed error and align all panels via workspace state

Consolidate `.git` presence detection into a shared `git_repo` module used by both the workspace state watcher and the command preflight helper, replacing duplicated local definitions.

Introduce `AppErrorCode::NotAGitRepository` (HTTP 422) and preflight eleven frontend-callable git commands (log, status, list-branches, diff, diff-with-branch, show-diff, show-file, push-info, list-remotes, list-all-branches, commit-branches) so non-git folders short-circuit with a structured error instead of leaking locale-dependent git stderr.

Frontend `isNotAGitRepoError` checks the error code first and falls back to a multi-language regex list centralized in `src/i18n/git-error-patterns.ts`, covering the nine languages git actually translates into.

Wire the git log panel to `workspaceState.isGitRepo` rather than a local cached flag, so running `git init` or deleting `.git` externally propagates through the watcher and refreshes the panel automatically.

src/i18n/git-error-patterns.ts

@@ -0,0 +1,29 @@
+/**
+ * Locale-independent patterns that identify a "not a git repository" error
+ * from the raw stderr of a failed git invocation.
+ *
+ * Git translates its error messages via gettext based on the **system**
+ * LC_MESSAGES locale, which may differ from the user's browser locale.
+ * Detection therefore needs patterns for every language git might emit on
+ * the server, not just the one the UI is localized into.
+ *
+ * These patterns are a belt-and-suspenders fallback. The primary detection
+ * path is the typed `not_a_git_repository` error code returned by backend
+ * commands wrapped with a filesystem preflight check (see
+ * `src-tauri/src/commands/folders.rs::ensure_git_repo`). Patterns only apply
+ * when an un-preflighted command leaks raw stderr to the client.
+ *
+ * Locales covered match git's own gettext translations. Arabic falls back to
+ * English in upstream git (no ar translation), so no separate pattern.
+ */
+export const NOT_A_GIT_REPO_PATTERNS: readonly RegExp[] = [
+  /not a git repository/i, // en
+  /不是\s*git\s*仓库/i, // zh-CN
+  /不是\s*git\s*儲存庫/i, // zh-TW
+  /git\s*リポジトリではありません/i, // ja
+  /git\s*저장소가\s*아닙니다/i, // ko
+  /kein\s*git[-\s]*repository/i, // de
+  /pas\s*(?:un|dans\s*un)\s*d[ée]p[oô]t\s*git/i, // fr
+  /no\s*es\s*un\s*repositorio\s*git/i, // es
+  /n[ãa]o\s*[ée]\s*um\s*reposit[oó]rio\s*git/i, // pt
+]