feat: public sharing links for households

Add hard-to-guess public URLs (/public/<token>) that show a read-only
meal status dashboard for each household. Only people with the link can
see the data — no login required.

- models.py: public_token + public_enabled columns on households,
  get_household_by_public_token(), generate_public_token(),
  set_public_enabled()
- meals.py: /public/<token> route, /admin/public-link for
  generate/disable/enable/regenerate
- templates/public.html: clean read-only public dashboard
- templates/public-not-found.html: 404 for invalid/disabled links
- templates/dashboard.html: admin UI with copy/regenerate/disable
- static/style.css: public page and URL box styles
- i18n.py: 18 new translation keys (en/fr/de)

models.py

@@ -86,6 +86,10 @@ def init_db() -> None:
             db.execute("ALTER TABLE households ADD COLUMN last_lunch_reminder TEXT DEFAULT ''")
         if "last_dinner_reminder" not in hh_cols:
             db.execute("ALTER TABLE households ADD COLUMN last_dinner_reminder TEXT DEFAULT ''")
+        if "public_token" not in hh_cols:
+            db.execute("ALTER TABLE households ADD COLUMN public_token TEXT DEFAULT ''")
+        if "public_enabled" not in hh_cols:
+            db.execute("ALTER TABLE households ADD COLUMN public_enabled INTEGER DEFAULT 1")
 
 
 # ── Households ────────────────────────────────────────────────────────────────
@@ -156,6 +160,39 @@ def update_reminder_sent(household_id: int, meal_type: str, date_str: str) -> No
                    (date_str, household_id))
 
 
+# ── Public sharing ───────────────────────────────────────────────────────────
+
+def get_household_by_public_token(token: str) -> dict | None:
+    """Look up a household by its public sharing token."""
+    with get_db() as db:
+        row = db.execute(
+            "SELECT * FROM households WHERE public_token = ? AND public_enabled = 1",
+            (token,),
+        ).fetchone()
+        return dict(row) if row else None
+
+
+def generate_public_token(household_id: int) -> str:
+    """Generate a new hard-to-guess public token for a household."""
+    import secrets
+    token = secrets.token_urlsafe(32)
+    with get_db() as db:
+        db.execute(
+            "UPDATE households SET public_token = ?, public_enabled = 1 WHERE id = ?",
+            (token, household_id),
+        )
+    return token
+
+
+def set_public_enabled(household_id: int, enabled: bool) -> None:
+    """Enable or disable the public sharing link for a household."""
+    with get_db() as db:
+        db.execute(
+            "UPDATE households SET public_enabled = ? WHERE id = ?",
+            (int(enabled), household_id),
+        )
+
+
 # ── Users ─────────────────────────────────────────────────────────────────────
 
 def get_user_by_id(user_id: int) -> dict | None: