fix(memory): exclude pinned issues from GetReadyWork

SQLite storage already excluded pinned issues from ready work
(bd-92u), but memory storage was missing this check. Pinned
issues are context markers, not actionable work items.

Closes bd-o9o.

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

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

internal/storage/memory/memory.go

@@ -902,6 +902,11 @@ func (m *MemoryStorage) GetReadyWork(ctx context.Context, filter types.WorkFilte
 	var results []*types.Issue
 
 	for _, issue := range m.issues {
+		// Skip pinned issues - they are context markers, not actionable work (bd-o9o)
+		if issue.Pinned {
+			continue
+		}
+
 		// Status filtering: default to open OR in_progress if not specified
 		if filter.Status == "" {
 			if issue.Status != types.StatusOpen && issue.Status != types.StatusInProgress {