feat(api): support explicit provider secret projection

src/langbot/pkg/api/http/controller/groups/provider/query.py

@@ -0,0 +1,15 @@
+from __future__ import annotations
+
+
+def resolve_include_secret(raw_value: str | None, *, permitted: bool) -> tuple[bool, str | None]:
+    """Resolve the optional secret projection query parameter."""
+
+    if raw_value is None:
+        return permitted, None
+
+    value = raw_value.strip().lower()
+    if value == 'false':
+        return False, None
+    if value == 'true':
+        return permitted, None
+    return False, 'include_secret must be either true or false'