feat: add admin endpoint to send digest emails for users

- Implemented a new endpoint `/admin/test/send-digest` in `admin_api.py` to trigger digest emails for specific users.
- Added a script `send_digest.py` to facilitate sending digest emails via the admin API.
- Enhanced the digest action handling in `digest_action_api.py` to support token peeking without consuming it.
- Updated the `send_digests` function in `digest_scheduler.py` to utilize the new `send_digest_for_user` function for sending emails.
- Introduced a new utility function `peek_token` in `digest_token.py` to validate tokens without consuming them.
- Modified the `ParentView.vue` component to handle digest actions upon receiving a digest token in the URL.
- Updated `.gitignore` to exclude sensitive certificate files.

backend/utils/digest_token.py

@@ -101,6 +101,40 @@ def validate_and_consume_token(token_id: str) -> DigestActionToken | None:
     return token
 
 
+def peek_token(token_id: str) -> DigestActionToken | None:
+    """
+    Validate a token (signature, expiry, not-used) WITHOUT consuming it.
+    Returns the token if valid, None otherwise.
+    """
+    token = get_token_by_id(token_id)
+    if not token or token.used:
+        return None
+
+    try:
+        expires_at = datetime.fromisoformat(token.expires_at)
+        if expires_at.tzinfo is None:
+            expires_at = expires_at.replace(tzinfo=timezone.utc)
+        if datetime.now(timezone.utc) > expires_at:
+            return None
+    except (ValueError, TypeError):
+        return None
+
+    payload = {
+        'id': token.id,
+        'user_id': token.user_id,
+        'child_id': token.child_id,
+        'entity_id': token.entity_id,
+        'entity_type': token.entity_type,
+        'action': token.action,
+        'expires_at': token.expires_at,
+    }
+    expected_sig = _sign(payload)
+    if not hmac.compare_digest(token.signature, expected_sig):
+        return None
+
+    return token
+
+
 def create_unsubscribe_token(user_id: str) -> str:
     """
     Create a simple signed unsubscribe token string (not persisted in DB).