🧪 Add tests for JobRateLimiter and make time deterministic

[adcondev]

🎯 What: The internal/server/rate_limit.go rate limiter was missing unit tests. Additionally, the existing implementation relied directly on time.Now() preventing deterministic behavior in tests.
📊 Coverage: I refactored the struct to have an injectable now func() time.Time (defaulting to time.Now) and added tests that cover all allowance branches: passing when under limits, failing when over, expiring older entries from the time window, behaving independently between IP clients, and defaulting effectively when now is nil. The line coverage on rate_limit.go is now 100%.
✨ Result: We now have deterministic testing preventing rate-limit logic regressions. Abuse behavior can be verified correctly.

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PR created automatically by Jules for task 3097189037211435559 started by @adcondev

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[github-actions]

⚡ Benchmark Results

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✅ All modified and coverable lines are covered by tests.

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