feat(app): select worktree base branch - #44906

Summary

• add a location-scoped API for listing local and remote Git branches, ordered by recent commit activity with bounded, case-insensitive server-side search
• let worktree creation accept a selected base branch while keeping the new checkout detached
• select the base branch directly from a searchable, scrollable from {branch} dropdown with debounced requests, persistent results, and project-selector styling
• persist the selected base branch per draft and protect Git invocation from treating branch names as command options

Validation

• bun typecheck in packages/app, packages/core, packages/server, packages/client, packages/protocol, and packages/schema
• repository pre-push typechecks across 32 packages
• bun typecheck:e2e in packages/app
• bun run test:unit in packages/app (530 passed)
• bun test test/worktree.test.ts test/vcs.test.ts in packages/core (27 passed)
• bun test test/vcs.test.ts in packages/core (8 passed, including recency ordering, case-insensitive search, result limits, and literal search metacharacters)
• bun test test/worktree.test.ts in packages/server (1 passed)
• bun test test/promise.test.ts in packages/client (23 passed)
• Playwright: new-session-workspace-branch.spec.ts (1 passed)

Requested by: @Brendonovich (Brendan via Slack)