fix: redact identity secrets through a public hook and mask issued agm_ tokens

Identity gains a redact field that the executor honours, so the OAuth
resolver no longer needs an executor subclass overriding private
internals. Opaque agm_ tokens issued by our authorization server are now
masked by the secret patterns wherever they appear in content.

src/aegis_gitea_mcp/gitea/executor.py

@@ -10,7 +10,7 @@ Security properties (all covered by tests):
 * path values are validated and percent-encoded (see :mod:`.encoding`);
 * redirects are never followed (a 3xx is an error of kind ``redirect``);
 * cookies are never stored, so one identity can not leak into another call;
-* the identity token, the configured Gitea token, the MCP bearer token, the
+* the identity token and ``Identity.redact``, the configured Gitea token, the MCP bearer token, the
   OAuth client secret, ``extra_secrets`` and secret values submitted in a
   request body are replaced with ``[REDACTED]`` in every result, always;
 * secret-pattern masking/blocking follows ``SECRET_DETECTION_MODE``, except for
@@ -412,7 +412,9 @@ class GiteaExecutor:
     # Sending
 
     def _secrets(self, identity: Identity, call: _Call) -> tuple[str, ...]:
-        return normalize_secrets([identity.token, *self._base_secrets, *call.call_secrets])
+        return normalize_secrets(
+            [identity.token, *identity.redact, *self._base_secrets, *call.call_secrets]
+        )
 
     async def _send(self, call: _Call, identity: Identity) -> ToolOutcome:
         headers = {