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/syncthing/detect_test.go

@@ -0,0 +1,9 @@
+package syncthing
+
+import "testing"
+
+func TestIsInstalled_NoPanic(t *testing.T) {
+	// IsInstalled should not panic regardless of environment.
+	// We don't assert the result since it depends on the host.
+	_ = IsInstalled()
+}