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>

internal/rpc/client.go

@@ -190,3 +190,23 @@ func (c *Client) RemoveLabel(args *LabelRemoveArgs) (*Response, error) {
 func (c *Client) Batch(args *BatchArgs) (*Response, error) {
 	return c.Execute(OpBatch, args)
 }
+
+// ReposList lists all cached repositories
+func (c *Client) ReposList() (*Response, error) {
+	return c.Execute(OpReposList, struct{}{})
+}
+
+// ReposReady gets ready work across all repositories
+func (c *Client) ReposReady(args *ReposReadyArgs) (*Response, error) {
+	return c.Execute(OpReposReady, args)
+}
+
+// ReposStats gets combined statistics across all repositories
+func (c *Client) ReposStats() (*Response, error) {
+	return c.Execute(OpReposStats, struct{}{})
+}
+
+// ReposClearCache clears the repository cache
+func (c *Client) ReposClearCache() (*Response, error) {
+	return c.Execute(OpReposClearCache, struct{}{})
+}