feat(board): add mgw:board sync — reconcile all board items with current .mgw/ state

[snipcodeit]

Summary

• Adds mgw:board sync as a fifth subcommand to mgw:board, enabling full board reconciliation after context resets or drift
• Iterates all .mgw/active/*.json state files, fetches board items in a single GraphQL bulk query, adds missing issues, and updates Status/AI Agent State/Phase/Milestone fields to match local state
• Implements diff-only writes (only changed fields are updated) and non-blocking per-item error handling with a reconciliation diff table output
• Documents the bulk reconciliation pattern in board-sync.md Consumers table

Closes #82

Milestone Context

• Milestone: v2 — Team Collaboration & Lifecycle Orchestration
• Phase: 16 — Team Awareness & Assignment
• Issue: 3 of 6 in milestone

Changes

.claude/commands/mgw/board.md

• Updated argument-hint and description frontmatter to include sync
• Updated <objective> block — now lists 5 subcommands with sync described
• parse_and_validate step: added sync to usage message and case statement
• New <step name="subcommand_sync"> process block with full reconciliation implementation:
  • Guard: board must be configured
  • Bulk GraphQL fetch of all board items via node(id: $BOARD_NODE_ID)
  • Per-issue loop: add missing items, diff Status/AI Agent State/Phase/Milestone, apply updates
  • Reconciliation diff table output with summary line
• Added 16 sync-specific entries to <success_criteria>

.claude/commands/mgw/workflows/board-sync.md

• Added board.md (sync) row to the Consumers table documenting the bulk reconciliation pattern

Test Plan

• Run /mgw:board sync with no board configured → "No board configured" error
• Run /mgw:board sync with empty .mgw/active/ → "Nothing to sync" clean exit
• Run /mgw:board sync with active issues and a configured board → reconciliation table printed
• Verify issues not on board are added via addProjectV2ItemById
• Verify Status field is updated when pipeline_stage differs from board Status value
• Verify AI Agent State is cleared when it has a stale value
• Verify Phase field is updated from phase:* label on the issue
• Verify Milestone field is updated from project.json milestone title lookup
• Verify per-item errors are logged in the diff table without stopping the loop
• Verify mgw:board usage message now includes sync in the subcommand list
• Confirm board-sync.md Consumers table includes the board.md (sync) row