v0.24.0 — Pre-testing observability: debug logging, diagnostic dump, startup self-test

- Add [DEBUG] logging across all modules (backup, storage, sync, selfupdate,
  monitor, notify, report, assets, setup) gated behind logging.level: "debug"
- Add /api/debug/dump endpoint returning full controller state JSON (debug only)
- Add startup self-test validating 9 subsystems (Docker, dirs, storage, hub,
  restic repos, metrics DB) with pass/warn/fail summary
- New packages: internal/selftest, internal/util
- Constructor/signature changes: debug bool params, logger params on
  RunHealthCheck and BuildReport, smart watchdog probe logging

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

controller/internal/util/strings.go

@@ -0,0 +1,12 @@
+package util
+
+import "strings"
+
+// TruncateStr truncates a string to maxLen characters, appending "..." if truncated.
+func TruncateStr(s string, maxLen int) string {
+	s = strings.TrimSpace(s)
+	if len(s) <= maxLen {
+		return s
+	}
+	return s[:maxLen] + "..."
+}