feat: Auto-migrate database on CLI version bump (bd-jgxi)

When CLI is upgraded (e.g., 0.24.0 → 0.24.1), the database version
is now automatically updated to match the CLI version during
PersistentPreRun. This fixes the recurring UX issue where bd doctor
shows version mismatch after every CLI upgrade.

Implementation:
- Added autoMigrateOnVersionBump() function in version_tracking.go
- Calls after trackBdVersion() in PersistentPreRun
- Best-effort and silent failures to avoid disrupting commands
- Only updates bd_version metadata field
- Includes comprehensive test coverage

Changes:
- cmd/bd/main.go: Call autoMigrateOnVersionBump() in PersistentPreRun
- cmd/bd/version_tracking.go: Implement auto-migration logic
- cmd/bd/version_tracking_test.go: Add tests for auto-migration

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

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

cmd/bd/version_tracking.go

@@ -1,10 +1,14 @@
 package main
 
 import (
+	"context"
 	"fmt"
+	"os"
 
 	"github.com/steveyegge/beads/internal/beads"
 	"github.com/steveyegge/beads/internal/configfile"
+	"github.com/steveyegge/beads/internal/debug"
+	"github.com/steveyegge/beads/internal/storage/sqlite"
 )
 
 // trackBdVersion checks if bd version has changed since last run and updates metadata.json.
@@ -112,3 +116,82 @@ func maybeShowUpgradeNotification() {
 	fmt.Println("💡 Run 'bd upgrade review' to see what changed")
 	fmt.Println()
 }
+
+// autoMigrateOnVersionBump automatically migrates the database when CLI version changes.
+// This function is best-effort - failures are silent to avoid disrupting commands.
+// Called from PersistentPreRun after trackBdVersion().
+//
+// bd-jgxi: Auto-migrate database on CLI version bump
+func autoMigrateOnVersionBump() {
+	// Only migrate if version upgrade was detected
+	if !versionUpgradeDetected {
+		return
+	}
+
+	// Find the beads directory
+	beadsDir := beads.FindBeadsDir()
+	if beadsDir == "" {
+		// No .beads directory - nothing to migrate
+		return
+	}
+
+	// Load config to get database path
+	cfg, err := configfile.Load(beadsDir)
+	if err != nil || cfg == nil {
+		// Config load failed or doesn't exist - skip migration
+		debug.Logf("auto-migrate: skipping migration, config load failed: %v", err)
+		return
+	}
+
+	// Get database path
+	dbPath := cfg.DatabasePath(beadsDir)
+
+	// Check if database exists
+	if _, err := os.Stat(dbPath); os.IsNotExist(err) {
+		// No database file - nothing to migrate
+		debug.Logf("auto-migrate: skipping migration, database does not exist: %s", dbPath)
+		return
+	}
+
+	// Open database to check current version
+	ctx := context.Background()
+	store, err := sqlite.New(ctx, dbPath)
+	if err != nil {
+		// Failed to open database - skip migration
+		debug.Logf("auto-migrate: failed to open database: %v", err)
+		return
+	}
+
+	// Get current database version
+	dbVersion, err := store.GetMetadata(ctx, "bd_version")
+	if err != nil {
+		// Failed to read version - skip migration
+		debug.Logf("auto-migrate: failed to read database version: %v", err)
+		_ = store.Close()
+		return
+	}
+
+	// Check if migration is needed
+	if dbVersion == Version {
+		// Database is already at current version
+		debug.Logf("auto-migrate: database already at version %s", Version)
+		_ = store.Close()
+		return
+	}
+
+	// Perform migration: update database version
+	debug.Logf("auto-migrate: migrating database from %s to %s", dbVersion, Version)
+	if err := store.SetMetadata(ctx, "bd_version", Version); err != nil {
+		// Migration failed - log and continue
+		debug.Logf("auto-migrate: failed to update database version: %v", err)
+		_ = store.Close()
+		return
+	}
+
+	// Close database
+	if err := store.Close(); err != nil {
+		debug.Logf("auto-migrate: warning: failed to close database: %v", err)
+	}
+
+	debug.Logf("auto-migrate: successfully migrated database to version %s", Version)
+}