fix(migrations): schema base 000 per DB vuoti, stamp head dopo create_all (#6)

upgrade head partiva dalla 001, che sa solo aggiungere colonne a tabelle
che assume gia' esistenti: su un DB davvero vuoto falliva subito. Nuova
000_base_schema.py (revision "000_base", down_revision None) crea lo
schema pre-001 esplicitamente (create_table, non Base.metadata.create_all,
che porterebbe gia' le colonne di 001-013 e farebbe fallire 001 su
"Duplicate column"). No-op se la tabella recipes esiste gia'
(sa.inspect(bind).has_table("recipes")). 001 ora ha down_revision =
"000_base".

setup.py: init-db e reset-db, dopo create_all/drop_all+create_all,
eseguono l'equivalente di "alembic stamp head" (nuovo _stamp_head(),
command.stamp con la config di src/backend/migrations/alembic.ini) cosi'
un DB nato da create_all non ritenta le migrazioni 001-013 al prossimo
deploy.

Test: catena upgrade head su SQLite vuoto, tabelle/colonne confrontate
con Base.metadata; DB con recipes gia' nello stato pre-001 -> upgrade
head non fallisce (000 no-op). _stamp_head si appoggia a
migrations/env.py, che costruisce una connessione propria da
settings.database_url (non modificabile dai test tramite l'engine
patchato di setup.py): nei test di setup.py e' quindi no-op via
monkeypatch, cosi' init-db/reset-db continuano a girare su SQLite senza
toccare un MySQL vero.

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

src/backend/api/routers/setup.py

@@ -9,6 +9,8 @@ import secrets
 from datetime import datetime, timedelta
 from pathlib import Path
 
+from alembic import command
+from alembic.config import Config
 from fastapi import APIRouter, HTTPException, Request, status
 from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
@@ -28,10 +30,24 @@ from src.backend.services.measurement_service import calculate_pass_fail
 
 router = APIRouter(prefix="/api/setup", tags=["setup"])
 
-_templates_dir = Path(__file__).resolve().parent.parent.parent / "templates"
+_backend_dir = Path(__file__).resolve().parent.parent.parent
+_templates_dir = _backend_dir / "templates"
+_alembic_ini = _backend_dir / "migrations" / "alembic.ini"
 templates = Jinja2Templates(directory=str(_templates_dir))
 
 
+def _stamp_head() -> None:
+    """Mark the schema as fully migrated - the equivalent of `alembic stamp
+    head` - after `Base.metadata.create_all()`.
+
+    A database that got its tables this way instead of through
+    `upgrade head` has no row in `alembic_version`; without this, its next
+    deploy would try to replay migrations 001-013 and fail on a column that
+    is already there (see migration 000_base_schema.py).
+    """
+    command.stamp(Config(str(_alembic_ini)), "head")
+
+
 # ---------------------------------------------------------------------------
 # Request schemas
 # ---------------------------------------------------------------------------
@@ -296,6 +312,7 @@ async def init_db(body: PasswordBody):
     await _require_not_initialised()
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)
+    _stamp_head()
     return {"status": "ok", "message": "Database tables created successfully"}
 
 
@@ -734,5 +751,6 @@ async def reset_db(body: ResetDbBody):
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.drop_all)
         await conn.run_sync(Base.metadata.create_all)
+    _stamp_head()
 
     return {"status": "ok", "message": "Database reset successfully"}