feat(close): Add --suggest-next flag to show newly unblocked issues (GH#679)

When closing an issue, the new --suggest-next flag returns a list of
issues that became unblocked (ready to work on) as a result of the close.

This helps agents and users quickly identify what work is now available
after completing a blocker.

Example:
  $ bd close bd-5 --suggest-next
  ✓ Closed bd-5: Completed

  Newly unblocked:
    • bd-7 "Implement feature X" (P1)
    • bd-8 "Write tests for X" (P2)

Implementation:
- Added GetNewlyUnblockedByClose to storage interface
- Implemented efficient single-query for SQLite using blocked_issues_cache
- Added SuggestNext field to CloseArgs in RPC protocol
- Added CloseResult type for structured response
- CLI handles both daemon and direct modes

Thanks to @kraitsura for the detailed feature request and design.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/rpc/server_issues_epics.go

@@ -555,6 +555,26 @@ func (s *Server) handleClose(req *Request) Response {
 	})
 
 	closedIssue, _ := store.GetIssue(ctx, closeArgs.ID)
+
+	// If SuggestNext is requested, find newly unblocked issues (GH#679)
+	if closeArgs.SuggestNext {
+		unblocked, err := store.GetNewlyUnblockedByClose(ctx, closeArgs.ID)
+		if err != nil {
+			// Non-fatal: still return the closed issue
+			unblocked = nil
+		}
+		result := CloseResult{
+			Closed:    closedIssue,
+			Unblocked: unblocked,
+		}
+		data, _ := json.Marshal(result)
+		return Response{
+			Success: true,
+			Data:    data,
+		}
+	}
+
+	// Backward compatible: just return the closed issue
 	data, _ := json.Marshal(closedIssue)
 	return Response{
 		Success: true,