feat: sistem de linkuri publice pentru proprietăți

Expune fluxul de rezervare anonimă printr-un link public partajabil
(/book/<slug>), cu calendar public, cod QR și proprietate demo publică.

Backend:
- slug + list_on_landing pe Property; utilitar slugify (diacritice RO,
  cuvinte rezervate, ban all-digit) + migrare idempotentă raw-DDL rulată
  din entrypoint; SQLite WAL + busy_timeout
- GET /public/properties/{slug_or_id}(+/spaces): rezolvare slug/ID, 404 uniform
- GET /public/spaces/{id}/busy: doar {start_time,end_time} (fără PII),
  pending+approved, tz-aware/interval>60z → 422, orfan/privat → 404
- availability: scrub user_name/title (fix scurgere PII)
- POST /public/bookings: overlap pending+approved, cap 5/email/spațiu/zi,
  rate-limit per-IP, suprimare notificări+email pe demo, email confirmare guest
- PATCH slug (409 duplicat / 422 format / 403 non-manager); guest_email EmailStr
- email guest la aprobare/respingere cu cod #RB-<id>
- teste noi: test_public.py + test_migrate_slug.py (33 teste)

Frontend:
- rută /book/:slug; PublicBooking rescris cu calendar grid manual
  (PublicCalendar + GuestBookingForm), 30min, 08-20, mobil day-view, RO
- card „Link public" în PropertyDetail: copy, edit slug, QR pe URL-ul cu ID
- secțiune proprietăți publice + CTA pe Landing; buton copy în Properties

Gate aprobat (U1-U3, G1 grid manual, G2 list_on_landing); G3-G5 în TODOS.md.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/app/db/session.py

@@ -1,16 +1,28 @@
 """Database session management."""
 from collections.abc import Generator
 
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, event
 from sqlalchemy.orm import Session, declarative_base, sessionmaker
 
 from app.core.config import settings
 
+_is_sqlite = "sqlite" in settings.database_url
+
 engine = create_engine(
     settings.database_url,
-    connect_args={"check_same_thread": False} if "sqlite" in settings.database_url else {},
+    connect_args={"check_same_thread": False} if _is_sqlite else {},
 )
 
+if _is_sqlite:
+    @event.listens_for(engine, "connect")
+    def _set_sqlite_pragma(dbapi_connection, connection_record) -> None:
+        """Enable WAL mode + a busy timeout so concurrent readers/writers
+        don't immediately hit 'database is locked' errors."""
+        cursor = dbapi_connection.cursor()
+        cursor.execute("PRAGMA journal_mode=WAL")
+        cursor.execute("PRAGMA busy_timeout=5000")
+        cursor.close()
+
 SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 
 Base = declarative_base()