feat(tenancy): add team invitation acceptance page

New standalone page at /store/{store_code}/invitation/accept?token=xxx
where invited team members can:
- Review their name and email (pre-filled from invitation)
- Set their password
- Accept the invitation

Page handles all routing modes (dev path, platform path, prod subdomain,
custom domain) via store context middleware. After acceptance, redirects
to the platform-aware store login page.

New service method get_invitation_info() validates the token and returns
invitation details without modifying anything.

Error states: expired token, already accepted, invalid token.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/tenancy/services/store_team_service.py

@@ -228,6 +228,52 @@ class StoreTeamService:
             logger.error(f"Error inviting team member: {str(e)}")
             raise
 
+    def get_invitation_info(self, db: Session, token: str) -> dict[str, Any] | None:
+        """
+        Get invitation details without accepting it.
+
+        Used by the acceptance page to pre-fill the form.
+        Returns None if token is invalid.
+        """
+        store_user = (
+            db.query(StoreUser)
+            .execution_options(include_deleted=True)
+            .filter(StoreUser.invitation_token == token)
+            .first()
+        )
+
+        if not store_user:
+            return None
+
+        user = store_user.user
+        store = store_user.store
+        role_name = store_user.role.name if store_user.role else "member"
+
+        # Check if already accepted
+        if store_user.invitation_accepted_at is not None:
+            return {
+                "valid": False,
+                "error": "already_accepted",
+                "store_name": store.name,
+            }
+
+        # Check expiration (7 days)
+        is_expired = False
+        if store_user.invitation_sent_at:
+            elapsed = datetime.utcnow() - store_user.invitation_sent_at
+            is_expired = elapsed > timedelta(days=7)
+
+        return {
+            "valid": not is_expired,
+            "error": "expired" if is_expired else None,
+            "email": user.email,
+            "first_name": user.first_name,
+            "last_name": user.last_name,
+            "store_name": store.name,
+            "store_code": store.store_code,
+            "role_name": role_name,
+        }
+
     def accept_invitation(
         self,
         db: Session,