feat: v6.0.0 PWA offline support

- manifest + icones, service worker (precache, network-first, Background Sync)

- module client FlowOffline (IndexedDB, queue, delta, flush) + hook editeur

- endpoints /api/v2/sync/{delta,batch,status} + moteur de sync (conflits LWW/orpheline/copie offline)

- migrations offline_sync_queue + sync_version (triggers)

- UI offline (banner, badge sync, toasts, icone dirty) + doc /help

- tests pytest (sync, migrations, SW, offline) + E2E Playwright; bump 6.0.0

app/routers/sync.py

@@ -0,0 +1,88 @@
+"""FlowDeck — /api/v2/sync endpoints (v6.0.0 PWA offline sync).
+
+Pairs with ``app/services/sync_engine.py``. All routes require an authenticated
+session (``flowdeck_session`` cookie).
+"""
+from __future__ import annotations
+
+import logging
+
+from fastapi import APIRouter, HTTPException, Query, Request
+from fastapi.responses import JSONResponse
+
+from app.auth.session import SessionManager
+from app.services.sync_engine import SyncEngine
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(prefix="/api/v2/sync", tags=["sync"])
+
+_engine = SyncEngine()
+
+
+def _user(request: Request) -> dict:
+    user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
+    if not user:
+        raise HTTPException(status_code=401, detail="Authentication required")
+    return user
+
+
+@router.get("/delta")
+async def sync_delta(
+    request: Request,
+    since: float = Query(default=0, description="Epoch seconds (ou ms) du dernier sync"),
+    workspace_id: int = Query(default=None),
+):
+    """Pull server-side changes since `since` (for the given workspace)."""
+    user = _user(request)
+    if workspace_id is None:
+        raise HTTPException(status_code=400, detail="workspace_id is required")
+    result = await _engine.get_delta(user["id"], since, workspace_id)
+    if result.get("error") == "forbidden":
+        return JSONResponse({"detail": "Forbidden"}, status_code=403)
+    return result
+
+
+@router.post("/batch")
+async def sync_batch(request: Request):
+    """Apply a batch of offline mutations and return per-mutation results."""
+    user = _user(request)
+    try:
+        body = await request.json()
+    except Exception:
+        raise HTTPException(status_code=400, detail="Invalid JSON body") from None
+
+    mutations = body.get("mutations") or []
+    device_id = body.get("device_id") or "unknown"
+    if not isinstance(mutations, list) or not mutations:
+        return {"results": [], "conflicts": [], "server_time": SyncEngine._now_epoch()}
+
+    result = await _engine.apply_batch(user["id"], mutations, device_id)
+    result["server_time"] = SyncEngine._now_epoch()
+    return result
+
+
+@router.get("/status")
+async def sync_status(request: Request, workspace_id: int = Query(default=None)):
+    """Synchronization status for the workspace (pending server queue, last sync)."""
+    user = _user(request)
+    from app.db import get_conn
+    with get_conn() as conn:
+        if not SyncEngine._can_access(conn, user["id"], workspace_id):
+            return JSONResponse({"detail": "Forbidden"}, status_code=403)
+        pending = conn.execute(
+            "SELECT COUNT(*) AS n FROM offline_sync_queue WHERE user_id=? AND status='pending'",
+            (user["id"],),
+        ).fetchone()["n"]
+        last = conn.execute(
+            "SELECT MAX(created_at) AS last FROM offline_sync_queue "
+            "WHERE user_id=? AND status='synced'",
+            (user["id"],),
+        ).fetchone()["last"]
+        return {
+            "pending_count": pending,
+            "last_sync": last,
+            "is_syncing": False,
+            "server_time": SyncEngine._now_epoch(),
+            "workspace_id": workspace_id,
+        }