Port compact tabs-registry device snapshots to main

[danshapiro]

Summary

• Port the Replace tabs registry with compact device snapshots #331 compact tabs-registry device snapshot payload from stale Stabilize dev green and canonical agent recovery #342 onto current origin/main.
• Replace append-only registry persistence with compact per-client open snapshots plus bounded closed-tab tombstones.
• Carry the protocol/client sync, device snapshot settings, and focused registry/client/server tests needed for the compact snapshot flow.

Source and scope

• Cherry-picked the Replace tabs registry with compact device snapshots #331 series from feature/tabs-registry-device-snapshots-dev: c3e64110, 2f41a345, 51c45db9, 19fdc0dc, f5fc24fa, e1004923, 13e02fe0, 9197b550, df10d046, 48a3b5de, 492c2642, b6dfaeb1.
• Intentionally dropped the unrelated coding CLI lab-note refresh that came along with the dev-stack history.
• Added a main-compatibility test adjustment so tab snapshot rehydration asserts current main session refs ({ provider, sessionId }) separately from serverInstanceId.
• Did not port feat: add multi-row tabs setting (per-client, off by default) #335 multi-row tabs or unrelated dev-stack payloads.

Verification

• FRESHELL_TEST_SUMMARY="focused compact tabs-registry device snapshots rerun" npm run test:vitest -- test/unit/server/tabs-registry/store.test.ts test/integration/server/tabs-registry-store.persistence.test.ts test/server/ws-tabs-registry.test.ts test/unit/client/store/tabRegistrySync.test.ts test/unit/client/store/tabRegistrySlice.test.ts test/unit/client/store/browserPreferencesPersistence.test.ts test/unit/client/store/crossTabSync.test.ts test/unit/client/lib/browser-preferences.test.ts test/unit/client/lib/known-devices.test.ts test/unit/client/components/TabsView.test.tsx test/unit/client/components/SettingsView.behavior.test.tsx test/e2e/settings-devices-flow.test.tsx test/e2e/tabs-view-search-range.test.tsx --run passed for the default-config client/e2e paths that Vitest selected: 10 files, 103 tests.
• npm run typecheck:client passed.
• npm run build:client passed, with existing Vite chunk-size/dynamic-import warnings.
• npm run lint exited 0 with 14 warnings and no errors.
• npm run typecheck:server fails before this branch's server changes are checked because current origin/main has TypeScript parse errors in server/mcp/freshell-tool.ts lines 73 and 472.
• Server-config tabs-registry tests through vitest.server.config.ts are blocked by the same npm run build:server failure in server global setup.

Supersedes

This PR supersedes the #331 compact tabs-registry device snapshots payload currently embedded in stale #342.