AGENTS.md supported; claude -p no longer hangs silently
Projects without a CLAUDE.md now fall back to AGENTS.md, configurable under Project instructions in /config (not yet on Bedrock, Vertex or Foundry). Fixed claude -p and Agent SDK sessions hanging with no result after an internal error, which now report the error and exit with code 1, plus a fix for conversations failing with "text content blocks must be non-empty" after --resume.

