feat(core): v5.0.0 command palette + FTS5 search, v5.2.0 versioned migrations

- Command palette Ctrl+K/Ctrl+P (base.html): universal search, fuzzy
  highlight, keyboard nav, quick actions. openQuickFind now opens it.
- GET /api/search endpoint + search service: unified pages + databases
  search, FTS5 with LIKE fallback, trash excluded, user-scoped.
- app/migrations.py: lightweight versioned migration runner (schema_version
  table); baseline schema = v1, new steps applied in order.
- Migration v2: missing indexes (users.email, user_oauth_tokens, etc).
- Migration v3: FTS5 pages_fts + sync triggers + backfill.
- VERSION + app.main -> 5.0.0; CHANGELOG + ROADMAP updated.
- +8 tests (tests/test_search_migrations.py). 259 passed (3 pre-existing
  PDF/weasyprint env failures unrelated).

app/main.py

@@ -14,7 +14,7 @@ from app.config import settings
 from app.db import init_db
 from app.middleware.csrf import CSRFMiddleware
 from app.middleware.security import ContentSecurityPolicyMiddleware, RateLimitMiddleware
-from app.routers import dashboard, board, notes, api, auth, webhooks, collections, my_tasks, workspace, library, public_api, admin, sharing, sidebar_config, export, agent
+from app.routers import dashboard, board, notes, api, auth, webhooks, collections, my_tasks, workspace, library, public_api, admin, sharing, sidebar_config, export, agent, search
 from app.routers.notifications import router as notifications_router
 from app.routers.collaboration import router as collaboration_router
 from app.routers.gitea import router as gitea_router
@@ -60,7 +60,7 @@ async def lifespan(_app: FastAPI):
 
 app = FastAPI(
     title="FlowDeck",
-    version="4.15.5",
+    version="5.0.0",
     docs_url="/docs" if settings.log_level == "DEBUG" else None,
     redoc_url=None,
     lifespan=lifespan,
@@ -92,6 +92,7 @@ app.include_router(export.router)
 app.include_router(notifications_router)
 app.include_router(collaboration_router)
 app.include_router(agent.router)
+app.include_router(search.router)
 
 app.mount("/static", StaticFiles(directory="static"), name="static")