fix(saas): eliminate 6 compiler warnings + stabilize directive complete

- Remove unused imports: Utc (billing/service), StatusCode (billing/handlers), Sha256 (billing/handlers)
- Fix unused variables: _db (scheduler), _e (payment WeChat error)
- Fix visibility: RegisterDeviceRequest pub(super) → pub (used in pub handler)
- Update STABILIZATION_DIRECTIVE.md: all 7 criteria met, downgrade to advisory
- Fix TRUTH.md §2.2: mark P0/P1 defects as resolved, update Admin pages count to 14

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

crates/zclaw-saas/src/scheduler.rs

@@ -37,7 +37,7 @@ pub fn parse_duration(s: &str) -> Result<Duration, String> {
 }
 
 /// 启动所有定时任务
-pub fn start_scheduler(config: &SchedulerConfig, db: PgPool, dispatcher: WorkerDispatcher) {
+pub fn start_scheduler(config: &SchedulerConfig, _db: PgPool, dispatcher: WorkerDispatcher) {
     for job in &config.jobs {
         let interval = match parse_duration(&job.interval) {
             Ok(d) => d,