feat(desktop): prepare verified macOS updates

[devswha]

Scope

Preparation-only checkpoint for the approved macOS arm64 updater. No installer, restart authority, browser capability, production key provisioning or release publication is enabled. Existing chat composer and locale edits are excluded and preserved locally.

Implemented

• Strict manifests, bounded resumable GitHub discovery and authorized HTTPS delivery.
• Real Minisign verification and read-only archive inspection with full file/mode/hash/link inventory.
• Private descriptor-anchored staging, atomic publication, revalidation and durable consent contracts.
• Single preparation owner with cancellation, scheduling and epoch-aware snapshots, connected only after healthy server startup.
• Compiled QA profile and private-CA binding; independent packaged payload/runtime identity checks.
• Prior release-artifact tooling and isolated probes, with their outstanding safety gates retained.

Verification

• Full npm run verify passed on the local worktree; existing unrelated UI changes were present for that run but are not in this PR.
• Rust 1.85.1 locked desktop tests: 164 passed; 1 explicit real-archive test ignored by default and run separately.
• Build binding: 9 passed. Isolated updater probe: 19 passed.
• Clippy all targets with warnings denied and cargo fmt check passed.
• Release tests: 224 passed, 10 Linux-only skips.
• Historical archive: all 20,673 inventory entries match the producer. This is compatibility evidence, not release/install or OS-floor acceptance.
• Private-CA HTTPS: default roots reject before HTTP; compiled-fixture trust succeeds. No insecure overrides.
• Independent archive/discovery/cache/coordinator reviews and cancellation/retirement regressions completed.

Remaining gates

Real macOS authorization approve/cancel and writer-exit proof, macOS 13 execution, current Linux package acceptance, installation/attempt recovery, authenticated main-view bridge, complete activity admission, safe manual restart, About UI and signed isolated A-to-B/data/GUI acceptance remain outstanding. Installation remains unavailable. See docs/MACOS-UPDATER-HANDOFF.md.

Final remote verification — 2026-09-07

All eight checks passed for ee8fa60: Node 22/24 verification, Linux server build and Ubuntu 22.04/24.04 acceptance, Linux deb/AppImage build including locked Tauri tests, and both Ubuntu packaged-server/GUI/installed-launcher checks. The earlier Linux-package acceptance item is now satisfied for this checkpoint. Additional local driver/wire E2E: 8 passed.

macOS authorization/writer-exit proof, actual macOS 13 execution, installation/recovery, authenticated bridge/activity admission, About UI and signed isolated A-to-B remain incomplete. This PR stays draft; no release or installation was performed.