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/protocol.go

@@ -3,6 +3,8 @@ package rpc
 import (
 	"encoding/json"
 	"time"
+
+	"github.com/steveyegge/beads/internal/types"
 )
 
 // Operation constants for all bd commands
@@ -124,8 +126,16 @@ type UpdateArgs struct {
 
 // CloseArgs represents arguments for the close operation
 type CloseArgs struct {
-	ID     string `json:"id"`
-	Reason string `json:"reason,omitempty"`
+	ID          string `json:"id"`
+	Reason      string `json:"reason,omitempty"`
+	SuggestNext bool   `json:"suggest_next,omitempty"` // Return newly unblocked issues (GH#679)
+}
+
+// CloseResult is returned when SuggestNext is true (GH#679)
+// When SuggestNext is false, just the closed issue is returned for backward compatibility
+type CloseResult struct {
+	Closed    *types.Issue   `json:"closed"`              // The issue that was closed
+	Unblocked []*types.Issue `json:"unblocked,omitempty"` // Issues newly unblocked by closing
 }
 
 // DeleteArgs represents arguments for the delete operation