feat(blocked): exclude pinned issues from bd blocked output

- Add Pinned field to Issue struct in types.go
- Create migration 023 to add pinned column with partial index
- Update SQLite GetBlockedIssues to filter WHERE pinned = 0
- Update Memory GetBlockedIssues to skip pinned issues
- Update schema.go with pinned column definition

Pinned issues are tracked but excluded from the blocked list to
reduce noise for issues that are intentionally parked.

Closes: beads-ei4

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

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

internal/storage/sqlite/ready.go

@@ -252,11 +252,13 @@ func (s *SQLiteStorage) GetStaleIssues(ctx context.Context, filter types.StaleFi
 }
 
 // GetBlockedIssues returns issues that are blocked by dependencies or have status=blocked
+// Note: Pinned issues are excluded from the output (beads-ei4)
 func (s *SQLiteStorage) GetBlockedIssues(ctx context.Context) ([]*types.BlockedIssue, error) {
 	// Use UNION to combine:
 	// 1. Issues with open/in_progress/blocked status that have dependency blockers
 	// 2. Issues with status=blocked (even if they have no dependency blockers)
 	// Use GROUP_CONCAT to get all blocker IDs in a single query (no N+1)
+	// Exclude pinned issues (beads-ei4)
 	rows, err := s.db.QueryContext(ctx, `
 		SELECT
 		    i.id, i.title, i.description, i.design, i.acceptance_criteria, i.notes,
@@ -273,6 +275,7 @@ func (s *SQLiteStorage) GetBlockedIssues(ctx context.Context) ([]*types.BlockedI
 		        AND blocker.status IN ('open', 'in_progress', 'blocked')
 		    )
 		WHERE i.status IN ('open', 'in_progress', 'blocked')
+		  AND i.pinned = 0
 		  AND (
 		      i.status = 'blocked'
 		      OR EXISTS (