fix(05): revise Phase 5 plans based on checker feedback — B1-B4, W1-W4

B1: Mark RESEARCH.md Open Questions as (RESOLVED) with decision text for all 3
B2: Backends now stateless — raise CloudConnectionError(reason=) only; API layer
    in cloud.py owns token refresh + DB update via _call_cloud_op helper
B3: Add Task 3 to Plan 05 — cloud connection + object cleanup on account deletion (SEC-09)
B4: Add frontend_url setting to Plan 01 Task 1; Plan 05 uses settings.frontend_url
    for OAuth callback redirects
W1: ROADMAP.md Phase 5 now correctly labels Plans 03+04 as Wave 3 (not Wave 2)
W2: Plan 06 invalid_grant test now asserts both 503 HTTP response AND DB REQUIRES_REAUTH
W3: Plan 06 Task 2 split into unit tests (4, cloud_utils.py) and integration tests (11, HTTP)
W4: Plan 07 adds Vitest tests for cloudConnections store (4 tests) and SettingsCloudTab
    mount test (2 tests) per CLAUDE.md testing protocol

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -193,8 +193,10 @@ Before any phase is marked complete, all three gates must pass:
 **Wave 1** — Test scaffold + dependencies
 - [ ] 05-01-PLAN.md — Wave 0 xfail stubs, conftest cloud fixtures, requirements.txt packages, config.py settings
 
-**Wave 2** — Shared utilities (parallel)
+**Wave 2** — Shared utilities
 - [ ] 05-02-PLAN.md — cloud_utils.py (SSRF + HKDF), cloud_cache.py (TTLCache), storage factory extension
+
+**Wave 3** — Cloud backends (parallel, both blocked on Wave 2 / Plan 05-02)
 - [ ] 05-03-PLAN.md — GoogleDriveBackend + OneDriveBackend (all 7 StorageBackend methods)
 - [ ] 05-04-PLAN.md — NextcloudBackend + WebDAVBackend (all 7 StorageBackend methods)