fix: deep bug hunt II — concurrency, security & optimization (25 files)

Critical: watchdog mutex panic safety, SetGeoAppOverride nil guard,
SSD-only app DB restore fallback.

High: double deploy race (atomic Deploying flag), delete/remove during
deploy guard, ScanStacks overwrite protection, FileBrowser mount mutex,
PushEvent history, PushOnce error handling, DB dump sync+close before
rename, restic retry fresh context, encrypt failure logging, cross-backup
path traversal validation, deepCopyStack completeness.

Security: constant-time API key comparison, login rate limiting (5/min),
git credential masking in logs, storage path prefix traversal fix.

Concurrency: MigrateEncryption lock ordering, SubdomainInUse I/O outside
lock, scheduler late-registered jobs, SQLite WAL verification, metrics
shutdown context, telemetry scan error logging, asset sync lock scope.

Optimization: streaming file copy for DB dumps, restic stats dedup,
atomic infra config copy.

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

controller/internal/metrics/collector.go

@@ -54,25 +54,25 @@ func (c *MetricsCollector) loop(ctx context.Context) {
 	defer ticker.Stop()
 
 	// Sample immediately on start
-	c.sample()
+	c.sampleWith(ctx)
 
 	for {
 		select {
 		case <-ctx.Done():
 			return
 		case <-ticker.C:
-			c.sample()
+			c.sampleWith(ctx)
 		}
 	}
 }
 
-func (c *MetricsCollector) sample() {
+func (c *MetricsCollector) sampleWith(ctx context.Context) {
 	sys := c.sampleSystem()
 	if err := c.store.InsertSystemMetrics(sys); err != nil {
 		c.logger.Printf("[WARN] Failed to store system metrics: %v", err)
 	}
 
-	containers := c.sampleContainers()
+	containers := c.sampleContainers(ctx)
 	if err := c.store.InsertContainerMetrics(containers); err != nil {
 		c.logger.Printf("[WARN] Failed to store container metrics: %v", err)
 	}
@@ -96,8 +96,8 @@ func (c *MetricsCollector) sampleSystem() SystemSample {
 	}
 }
 
-func (c *MetricsCollector) sampleContainers() []ContainerSample {
-	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+func (c *MetricsCollector) sampleContainers(parentCtx context.Context) []ContainerSample {
+	ctx, cancel := context.WithTimeout(parentCtx, 30*time.Second)
 	defer cancel()
 
 	cmd := exec.CommandContext(ctx, "docker", "stats", "--no-stream",