Add HSTS, gzip, Ntfy notifications, and paginate entries endpoint

- nginx: add HSTS (max-age=31536000) and gzip for text/css/js/json
- entries: add limit/offset query params (default 200, max 1000)
- Ntfy: wire NTFY_URL/NTFY_TOKEN through env; notify on startup, new
  registration, admin login, user disable, and user delete
- httpx==0.28.1 added for async Ntfy HTTP calls

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

backend/app/routers/entries.py

@@ -1,4 +1,4 @@
-from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi import APIRouter, Depends, HTTPException, Query, status
 from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 
@@ -33,6 +33,8 @@ def _calc_stats(entries: list[Entry]) -> BottleStats:
 
 @router.get("", response_model=list[EntryResponse])
 async def list_entries(
+    limit: int = Query(default=200, ge=1, le=1000),
+    offset: int = Query(default=0, ge=0),
     db: AsyncSession = Depends(get_db),
     current_user: User = Depends(get_current_user),
 ):
@@ -40,6 +42,8 @@ async def list_entries(
         select(Entry)
         .where(Entry.user_id == current_user.id)
         .order_by(Entry.date.desc(), Entry.created_at.desc())
+        .limit(limit)
+        .offset(offset)
     )
     return result.scalars().all()