[Watch] Add --verbose flag for debugging empty board and silent failures #781

Add --verbose flag to squad watch for debugging

Problem

When squad watch shows "Board is clear — Ralph is idling", users have no way to understand WHY. There's no logging of:

• What GitHub API calls were made
• What issues/PRs were found vs filtered
• Why the board is considered empty
• What --agent-cmd was resolved to
• Auth status (which gh account is active)

Proposed solution

Add a --verbose flag that outputs detailed diagnostic information:

squad watch --execute --verbose

Verbose output should include:

1. Startup diagnostics: repo detected, auth account, platform (github/ado)
2. Per-round details: API calls made, issues found, filter results, why each was included/excluded
3. Execute details: agent command being used, issues selected for execution, dispatch mode
4. Timing: round duration, API latency
5. Warnings: auth issues, missing labels, rate limit status

Example verbose output

[verbose] Repo: owner/repo (github)
[verbose] Auth: tamirdresher (gh CLI)
[verbose] Round 1 starting...
[verbose] gh issue list --label squad --state open → 5 issues
[verbose]   #42: "Fix auth bug" → squad:data (assigned, has PR) → skip
[verbose]   #43: "Research new lib" → squad:seven (no assignee) → ACTIONABLE
[verbose] gh pr list --state open → 2 PRs
[verbose]   PR #100: draft, squad/42-fix-auth → skip (draft)
[verbose]   PR #101: review requested → ACTIONABLE
[verbose] Board: 1 untriaged, 1 review-needed, 0 ready-to-merge
[verbose] Execute: dispatching #43 via agent-cmd "copilot ..."
[verbose] Round 1 complete (3.2s)

Also fix

• Warn when positional args are passed (they're ignored)
• Print --agent-cmd at startup so users can verify
• Surface auth errors instead of silently returning empty board