[Bug] Watch reports 'Board is clear' when GitHub API rate limit is hit #806

Problem

When squad watch hits a GitHub API rate limit, capabilities (triage, two-pass, execute, board) return empty data. The watch loop then reports:

📋 Board is clear — Ralph is idling

This is misleading — the board isn't clear, the API just can't be reached.

Observed behavior

✗ [11:57:35 AM] Check failed: GraphQL: API rate limit already exceeded for user ID 188938611.
⚠ [11:57:36 AM] two-pass: two-pass error: GraphQL: API rate limit already exceeded
⚠ [11:57:36 AM] execute: execute error: GraphQL: API rate limit already exceeded
📋 Board is clear — Ralph is idling  ← WRONG, should say rate-limited

Expected behavior

When API errors occur, watch should:

1. Report: ⚠ API rate limited — skipping this round (retry in {interval})
2. NOT report 'Board is clear' — that implies no work exists
3. Automatically increase interval (exponential backoff) until rate limit resets
4. Check gh api rate_limit to show when limit resets

Additional context

• EMU accounts (_microsoft suffix) have stricter rate limits
• 2-minute interval with 4+ capabilities = 12+ API calls per 8 minutes
• The circuit-breaker capability exists but doesn't catch this case