v0.3.0: fix HTTP client leak, add tests and CI pipeline

Reuse a single long-poll HTTP client instead of creating one per
Events() call (~every 30s). Make TLS skip-verify configurable via
syncthing_insecure_tls. Log previously swallowed config errors.
Add unit tests for all monitor trackers, config, and state logic.
Add CI workflow (vet, golangci-lint, govulncheck, go test -race).

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

internal/tray/menu.go

@@ -208,7 +208,9 @@ func (a *App) toggleSetting(field *bool, item *systray.MenuItem) {
 	} else {
 		item.Uncheck()
 	}
-	_ = config.Save(cfg)
+	if err := config.Save(cfg); err != nil {
+		log.Printf("config save error: %v", err)
+	}
 }
 
 func (a *App) rediscoverAPIKey() {
@@ -227,6 +229,8 @@ func (a *App) rediscoverAPIKey() {
 	a.mu.Unlock()
 
 	a.client.SetAPIKey(key)
-	_ = config.Save(a.cfg)
+	if err := config.Save(a.cfg); err != nil {
+		log.Printf("config save error: %v", err)
+	}
 	log.Printf("re-discovered API key")
 }