feat(list): add --pinned and --no-pinned filter flags

Add ability to filter issues by their pinned status in bd list command.

- Add pinned column to issues table via migration 023
- Add Pinned field to Issue struct and IssueFilter
- Update all storage layer queries to include pinned column
- Add --pinned flag to show only pinned issues
- Add --no-pinned flag to exclude pinned issues
- Update RPC layer to forward pinned filter to daemon mode
- Add pinned to allowedUpdateFields for bd update support

Resolves: beads-p8e

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

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

internal/storage/sqlite/migrations.go

@@ -39,6 +39,7 @@ var migrationsList = []Migration{
 	{"edge_consolidation", migrations.MigrateEdgeConsolidation},
 	{"migrate_edge_fields", migrations.MigrateEdgeFields},
 	{"drop_edge_columns", migrations.MigrateDropEdgeColumns},
+	{"pinned_column", migrations.MigratePinnedColumn},
 }
 
 // MigrationInfo contains metadata about a migration for inspection
@@ -85,6 +86,7 @@ func getMigrationDescription(name string) string {
 		"edge_consolidation":           "Adds metadata and thread_id columns to dependencies table for edge schema consolidation (Decision 004)",
 		"migrate_edge_fields":          "Migrates existing issue fields (replies_to, relates_to, duplicate_of, superseded_by) to dependency edges (Decision 004 Phase 3)",
 		"drop_edge_columns":            "Drops deprecated edge columns (replies_to, relates_to, duplicate_of, superseded_by) from issues table (Decision 004 Phase 4)",
+		"pinned_column":                 "Adds pinned column for flagging important issues (bd-p8e)",
 	}
 	
 	if desc, ok := descriptions[name]; ok {