chore: Critical test coverage gaps

[nfebe]

Problem

Several core packages have zero or near-zero test coverage:

Package	Coverage	Risk
internal/proxy	0%	Orchestrator logic untested
internal/scheduler	0%	Cron/backup scheduling untested
internal/system	0%	Services manager untested
internal/traffic	0%	Traffic analysis untested
internal/watcher	0%	File watcher untested
internal/security	~5%	Security package nearly untested
internal/backup	~30%	Backup logic partially tested
internal/api (handlers)	~15%	Most API handlers untested

Overall: 28 test files vs 61 packages.

Impact

Regressions go undetected. Refactoring is risky. Security-critical code paths (auth, backup, proxy) lack verification.

Proposed Fix

Priority order for adding tests:

1. internal/security — directly security-relevant
2. internal/api handlers — the public attack surface
3. internal/backup — data loss risk
4. internal/proxy — misconfig = downtime
5. internal/scheduler — silent failures

Target: 60%+ coverage on security and API packages.