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/rpc/server_issues_epics.go

@@ -694,6 +694,9 @@ func (s *Server) handleList(req *Request) Response {
 	filter.PriorityMin = listArgs.PriorityMin
 	filter.PriorityMax = listArgs.PriorityMax
 
+	// Pinned filtering (bd-p8e)
+	filter.Pinned = listArgs.Pinned
+
 	// Guard against excessive ID lists to avoid SQLite parameter limits
 	const maxIDs = 1000
 	if len(filter.IDs) > maxIDs {