Previously unblock only checked for blocked=true. Stories stuck in
merge with a merge_failure field were not considered "blocked" and
unblock refused to act. Now it clears both blocked and merge_failure,
and reports which fields were cleared.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Add `unblock` bot command (chat + web UI slash command) that clears the
`blocked` flag and resets `retry_count` to 0 in story front matter
- Works across all pipeline stages (1_backlog through 6_archived)
- Returns confirmation with story name and ID, or clear error if story
is not found or not blocked
- Expose `unblock_story` MCP tool for programmatic use by agents
- Make `chat::commands::unblock` module pub(crate) so story_tools can
call `unblock_by_number`
- Add 8 unit tests covering registration, validation, core logic, and
edge cases (not-found, not-blocked, any stage, story ID in response)
- Update MCP tools list test: 49 → 50 tools
dave