Slice 6: right-click command menu + git write actions

git boundary: Pull/Push/Commit/DiscardAll (discard is 1.4-destructive). Scanner.RefreshRepo re-scans one repo after a mutation. Service GitFetch/GitPull/GitPush/GitCommit/GitDiscard record a git-* activity event and refresh on success; service.New takes a refresh hook. HTTP POST /api/repo/git. New <repo-menu> overlay with plain-language commands (Get latest/Publish/Check for updates/Save my work/Set active/Ask Claude to switch/Copy path/Discard all changes), summoned by repo-list's repo:contextmenu. Added service test for commit/discard on a temp repo. Verified the menu live for safe commands.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/mcp/mcp_test.go

@@ -42,7 +42,7 @@ func TestMCPRoundTrip(t *testing.T) {
 	scanner := repos.NewScanner(g, log, []string{root}, 3, nil, time.Minute, false)
 	scanner.Refresh(context.Background())
 
-	svc := service.New(g, scanner.Index, activity.New(log, 200), nil)
+	svc := service.New(g, scanner.Index, activity.New(log, 200), nil, scanner.RefreshRepo)
 	srv := NewServer(svc, "test")
 
 	// Wire an in-memory client<->server session.