Checkpoint: password reset, rule expiry, migrations

- Self-service and admin password-change endpoints
  (PUT /v1/auth/password, PUT /v1/accounts/{id}/password)
- Policy rule time-scoped expiry (not_before / expires_at)
  with migration 000006 and engine filtering
- golang-migrate integration; embedded SQL migrations
- PolicyRecord fieldalignment lint fix

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/db/migrate.go

@@ -21,7 +21,7 @@ var migrationsFS embed.FS
 // LatestSchemaVersion is the highest migration version defined in the
 // migrations/ directory.  Update this constant whenever a new migration file
 // is added.
-const LatestSchemaVersion = 5
+const LatestSchemaVersion = 6
 
 // newMigrate constructs a migrate.Migrate instance backed by the embedded SQL
 // files.  It opens a dedicated *sql.DB using the same DSN as the main