Adopt PromptKit profile inheritance

docs/policy/architecture.md

@@ -50,8 +50,10 @@ directly.
 - Prompts receive curated module packages, never unbounded raw weather payloads.
 - Every execution validates the exact prompt version and output contract before
   collection. The selected profile is configured explicitly or declared by the
-  prompt; unsupported direct-key profiles and missing reported credentials fail
-  before collection.
+  prompt; profiles requiring unsupported direct API keys fail before collection.
+  A profile may have an empty backend identity when it supplies an endpoint;
+  PromptKit resolves inherited profiles and optional credential sources when it
+  executes them.
 - Prompt and profile validation completes before weather collection. Raw output
   is validated before template rendering.
 - Comparison validates every explicit profile before collection, prepares one