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/storage/memory/memory.go

@@ -1184,6 +1184,58 @@ func (m *MemoryStorage) GetStaleIssues(ctx context.Context, filter types.StaleFi
 	return stale, nil
 }
 
+// GetNewlyUnblockedByClose returns issues that became unblocked when the given issue was closed.
+// This is used by the --suggest-next flag on bd close (GH#679).
+func (m *MemoryStorage) GetNewlyUnblockedByClose(ctx context.Context, closedIssueID string) ([]*types.Issue, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	var unblocked []*types.Issue
+
+	// Find issues that depend on the closed issue
+	for issueID, deps := range m.dependencies {
+		issue, exists := m.issues[issueID]
+		if !exists {
+			continue
+		}
+
+		// Only consider open/in_progress, non-pinned issues
+		if issue.Status != types.StatusOpen && issue.Status != types.StatusInProgress {
+			continue
+		}
+		if issue.Pinned {
+			continue
+		}
+
+		// Check if this issue depended on the closed issue
+		dependedOnClosed := false
+		for _, dep := range deps {
+			if dep.DependsOnID == closedIssueID && dep.Type == types.DepBlocks {
+				dependedOnClosed = true
+				break
+			}
+		}
+
+		if !dependedOnClosed {
+			continue
+		}
+
+		// Check if now unblocked (no remaining open blockers)
+		blockers := m.getOpenBlockers(issueID)
+		if len(blockers) == 0 {
+			issueCopy := *issue
+			unblocked = append(unblocked, &issueCopy)
+		}
+	}
+
+	// Sort by priority ascending
+	sort.Slice(unblocked, func(i, j int) bool {
+		return unblocked[i].Priority < unblocked[j].Priority
+	})
+
+	return unblocked, nil
+}
+
 func (m *MemoryStorage) AddComment(ctx context.Context, issueID, actor, comment string) error {
 	return nil
 }