fix(app): backport session rename and tab menu fixes to v1 - #46116

Summary

Backport the session-title and tab-menu fixes to V1 (dev). Both reported bugs reproduced on the V1 API: Enter saved the heading, blur discarded it, and right-clicking a session tab opened no menu.

• Save edited session headings on blur; retain Escape cancellation, pending-save protection, empty-title handling, and drafts after failed saves.
• Add Rename / Close tab to the session-tab context menu using the existing V1 actions.
• Preserve focus handoff, hide hover previews while the menu is open, and allow inactive-tab renaming without switching sessions.

V2 counterpart: #46113
Original report: https://x.com/yeargun24/status/2093599753497874795

Validation

• 8 new V1 browser regressions pass: Enter, Tab, click outside, Escape, empty titles, failed saves, keyboard context menu, persistence after reload, inactive-tab rename, and closing without deletion.
• 4 adjacent browser tests pass: cross-server closing, legacy routes, mousedown navigation, and visible tab keyboard order.
• 7 tab gesture/order unit tests pass.
• App bun run typecheck, Prettier, and git diff --check pass.
• Production snapshot: all 8 regressions and 6 tab-switch benchmark cases pass. Three samples per mode: cold stable-paint median 53.2 → 59.4 ms; warm 27.2 → 27.1 ms; zero blank/wrong-destination samples. The small shared-host sample cannot establish a reliable performance regression.
• A targeted E2E typecheck is blocked by two existing part.text optionality errors in the unchanged shared fixture e2e/smoke/session-timeline.fixture.ts:233-234; no errors point to the new spec.

Browser tests use the real app in Chromium with fixture-backed V1 API responses. Native macOS desktop behavior was not exercised.

Requested by: @Brendonovich (Brendan via Slack)