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/config/paths.go

@@ -2,7 +2,18 @@ package config
 
 import "path/filepath"
 
+// configDirOverride allows tests to redirect config I/O to a temp directory.
+var configDirOverride string
+
+// configDir returns the override dir if set, otherwise the platform default.
+func configDir() string {
+	if configDirOverride != "" {
+		return configDirOverride
+	}
+	return ConfigDir()
+}
+
 // ConfigPath returns the path to config.json.
 func ConfigPath() string {
-	return filepath.Join(ConfigDir(), "config.json")
+	return filepath.Join(configDir(), "config.json")
 }