feat: Add bd repos multi-repo commands and fix bd ready for in_progress issues

- Add 'bd repos' command for multi-repository management (bd-123)
  - bd repos list: show all cached repositories
  - bd repos ready: aggregate ready work across repos
  - bd repos stats: combined statistics across repos
  - bd repos clear-cache: clear repository cache
  - Requires global daemon (bd daemon --global)

- Fix bd ready to show in_progress issues (bd-165)
  - bd ready now shows both 'open' and 'in_progress' issues with no blockers
  - Allows epics/tasks ready to close to appear in ready work
  - Critical P0 bug fix for workflow

- Apply code review improvements to repos implementation
  - Use strongly typed RPC responses (remove interface{})
  - Fix clear-cache lock handling (close connections outside lock)
  - Add error collection for per-repo failures
  - Add context timeouts (1-2s) to prevent hangs
  - Add lock strategy comments

- Update documentation (README.md, AGENTS.md)
- Add comprehensive tests for both features

Amp-Thread-ID: https://ampcode.com/threads/T-1de989a1-1890-492c-9847-a34144259e0f
Co-authored-by: Amp <amp@ampcode.com>

AGENTS.md

@@ -154,6 +154,13 @@ bd restore <id>  # View full history at time of compaction
 # Import with collision detection
 bd import -i .beads/issues.jsonl --dry-run             # Preview only
 bd import -i .beads/issues.jsonl --resolve-collisions  # Auto-resolve
+
+# Multi-repo management (requires global daemon)
+bd repos list                    # List all cached repositories
+bd repos ready                   # View ready work across all repos
+bd repos ready --group           # Group by repository
+bd repos stats                   # Combined statistics
+bd repos clear-cache             # Clear repository cache
 ```
 
 ### Workflow