fix(delegate): flatten content blocks in live overlay tail + AUTHOR_MAP

Follow-up on the cherry-picked content-block fix. _extract_output_tail
(the live subagent overlay) still used crude str(content), which renders
a "[{'type': 'text'...}]" blob and — worse — mislabels a block-wrapped
"Error: ..." result as is_error=False. Route it through the same
_stringify_tool_content helper so error detection and previews work at
both consumer sites.

- delegate_tool.py: _extract_output_tail uses _stringify_tool_content
- tests: add _extract_output_tail content-block test (error detection +
  clean preview)
- release.py: AUTHOR_MAP entry for randomsnowflake (CI gate)

scripts/release.py

@@ -45,6 +45,7 @@ ACP_REGISTRY_MANIFEST = REPO_ROOT / "acp_registry" / "agent.json"
 
 # Auto-extracted from noreply emails + manual overrides
 AUTHOR_MAP = {
+    "al@randomsnowflake.me": "randomsnowflake",
     "834740219@qq.com": "ViewWay",
     "harjoth.khara@gmail.com": "harjothkhara",
     "129007007+HeLLGURD@users.noreply.github.com": "HeLLGURD",