Add pinned column to the issues table to support persistent context markers
that should not be treated as work items (bd-7h5).
Changes:
- Add pinned column to schema.go CREATE TABLE
- Add migration 023_pinned_column.go for existing databases
- Update all issue queries to include pinned column
- Update scanIssues and scanIssuesWithDependencyType to handle pinned field
- Add Pinned field to types.Issue struct with JSON serialization
- Fix migrations_test.go to include pinned in legacy schema test
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
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