chore: remove issue ID references from comments and changelogs

Strip (bd-xxx), (gt-xxx) suffixes from code comments and changelog
entries. The descriptions remain meaningful without the ephemeral
issue IDs.

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

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

internal/storage/sqlite/migrations/027_gate_columns.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 )
 
-// MigrateGateColumns adds gate-related columns to the issues table for async coordination (bd-udsi).
+// MigrateGateColumns adds gate-related columns to the issues table for async coordination.
 // Gate fields enable agents to wait on external conditions (CI completion, human approval, etc.)
 func MigrateGateColumns(db *sql.DB) error {
 	columns := []struct {