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>

README.md

@@ -12,8 +12,10 @@
   <img src="https://img.shields.io/badge/Platform-Windows%20|%20Linux%20|%20macOS-informational" alt="Platform: Windows | Linux | macOS" />
   <img src="https://img.shields.io/badge/license-MIT-green" alt="MIT License" />
   <br />
-  <a href="https://git.davoryn.de/calic/syncwarden/releases"><img src="https://img.shields.io/badge/release-v0.2.0-blue?logo=gitea&logoColor=white" alt="Latest Release" /></a>
-  <a href="https://git.davoryn.de/calic/syncwarden/actions"><img src="https://img.shields.io/badge/CI-Gitea%20Actions-success?logo=gitea&logoColor=white" alt="CI" /></a>
+  <a href="https://git.davoryn.de/calic/syncwarden/releases"><img src="https://img.shields.io/badge/release-v0.3.0-blue?logo=gitea&logoColor=white" alt="Latest Release" /></a>
+  <a href="https://git.davoryn.de/calic/syncwarden/actions"><img src="https://img.shields.io/badge/tests-passing-brightgreen?logo=gitea&logoColor=white" alt="Tests" /></a>
+  <a href="https://git.davoryn.de/calic/syncwarden/actions"><img src="https://img.shields.io/badge/golangci--lint-passing-brightgreen?logo=go&logoColor=white" alt="golangci-lint" /></a>
+  <a href="https://git.davoryn.de/calic/syncwarden/actions"><img src="https://img.shields.io/badge/govulncheck-clean-brightgreen?logo=go&logoColor=white" alt="govulncheck" /></a>
 </p>
 
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