feat(app): add per-session permission mode to composer footer - #53739

Summary

Adds a Permissions dropdown to the end of the composer footer so a session can switch between Ask for approval and Auto-accept without changing the app-wide setting.

• Each session's choice is stored client-side in settings (permissions.sessions), keyed by server scope and root session ID. Sessions without a choice still follow the existing app-wide Auto-accept permissions setting, so the Settings toggle and mod+shift+a command become the default.
• Subagent requests follow their root session's mode. The footer reads and writes the root's mode when you're viewing a child session.
• The auto-approver still replies once to asked requests, so config deny rules stay enforced; it now decides per request instead of using one global flag. The permission dock and tab badge use the same per-session check.

Stacked on the composer footer

#49500 (composer workspace footer) was closed without merging, so the first commit ports it onto current v2 and keeps its original author:

• Since refactor(app): move GUI features into built-in extensions #52369 moved the session move menu into gui-extensions, the footer's menu now lives in the app as session/composer/workspace-menu.tsx, using the shared WorkspaceSubmenu.
• The new-session selector keeps current v2's own worktree search instead of the old submenu refactor.
• The menu's eligible gate was dropped because workspaceMoveEligible no longer exists. The menu is now blocked only while the session is running, which matches the extension's menu.

The second commit adds the dropdown.

Validation

• bun run typecheck in packages/app
• Unit tests: src/settings, src/session
• E2E: multi-server.spec.ts (the existing auto-accept keepers plus a new case), composer.spec.ts, mobile-composer-submit-focus.spec.ts, session-location-sync.spec.ts, and session-queue.spec.ts all pass. One session-queue typing case failed once and then passed 3/3 when repeated.
• The new e2e case checks that a session set to Auto-accept approves its subagent's request but not another session's. It fails if the mode is not resolved through the root session.
• Checked light, dark, and 420px-wide layouts with screenshots from the mock-server fixture. The screenshots are in the Slack thread.
• The production session benchmark from packages/app/AGENTS.md was not run.

Requested by: @Brendonovich (Brendan via Slack)