Add bulk delete for sessions in the sidebar

[dhilgaertner]

Summary

• Adds a Select toggle to the session sidebar; checked rows reveal a bulk action bar with Cancel / Delete (N) and a single confirmation dialog.
• Reuses the existing SessionService.deleteSession cascade (worktrees, branches, terminals, hook state, persistence) by iterating appState.onDeleteSession serially — no AppState or service changes.
• Mirrors the existing TicketBoardView selection pattern so the UX is consistent. Single-session deletion via context menu / detail-view button is unchanged.

Closes #191

Test plan

• make build succeeds
• swift test --package-path Packages/CrowUI — 22/22 passing, including 5 new buildBulkMessage tests
• Click the new ✓ toolbar button in the sidebar; confirm checkboxes appear on rows in Active / Reviews / In Review / Completed sections (and not on Manager / Allow List / Ticket Board / dividers).
• Select 2-3 sessions across different sections; confirm action bar appears with correct count.
• Click Delete (N) → confirm bulk alert message reflects worktree/main-checkout counts. Cancel preserves selection.
• Confirm delete → all selected sessions removed, worktree dirs gone (git worktree list), feature branches deleted (protected branches preserved), selection mode exits.
• In selection mode, clicking a row body still navigates to the detail view; only checkbox tap toggles selection.
• Click toolbar Cancel (✗ icon) — checkboxes disappear and selection clears.

🤖 Generated with Claude Code

[dgershman]

Code & Security Review

Critical Issues

None.

Security Review

Strengths:

• Destructive bulk operation is gated behind a confirmation dialog — users must explicitly confirm before any sessions/worktrees/branches are deleted.
• Main-repo checkouts and protected branches (main, master, develop, etc.) are preserved via the existing isMainRepoCheckout guard — the bulk path reuses the same cascade as single-session deletion, so no new bypass vectors are introduced.
• Serial iteration through onDeleteSession reuses the existing validated deletion pipeline. No new shell/git commands, no new file system operations.
• No secrets, no user input passed to shell commands, no injection surface.

Concerns:

• None identified.

Code Quality

Well done:

• Clean separation: buildBulkMessage is a pure, testable static method on the existing DeleteSessionMessageBuilder enum. 5 new tests cover the key message permutations (no worktrees, singular, real worktrees, mixed, main-only).
• BulkDeleteSessionsAlert follows the same ViewModifier pattern as DeleteSessionAlert, keeping the approach consistent.
• SessionRow gains selection mode cleanly: the existing row content is extracted into rowContent, and the checkbox/HStack wrapper is only added when isSelectionMode is true. Default parameter values (isSelectionMode: false, selectedSessionIDs: nil) preserve backward compatibility.
• Stable deletion order via sortedSnapshot — processes sessions in their current list order rather than arbitrary Set iteration.

Minor observations (non-blocking):

• If sessions are deleted externally (e.g., via CLI crow delete-session) between the user tapping "Delete" and the async loop executing, stale IDs become silent no-ops in SessionService.deleteSession. This is harmless but could be mildly confusing. A future enhancement could filter selectedIDs against appState.sessions at execution time — but this is not a bug today.
• The selectedSessionIDs binding on SessionRow is an optional Binding<Set<UUID>>?. This works but is slightly unusual — a non-optional binding with a no-op default (e.g., .constant([])) paired with the existing isSelectionMode bool would also work. Current approach is fine.

Summary Table

Priority	Issue
Green	Stale selection IDs become silent no-ops if sessions deleted externally — cosmetic, not a bug
Green	Optional binding pattern on SessionRow is functional but slightly unconventional

Recommendation: Approve. The PR is well-structured, reuses existing deletion infrastructure, includes good test coverage, and introduces no security concerns. The UI additions (toolbar toggle, checkbox column, bulk action bar, confirmation dialog) are clean and consistent with existing patterns.