[SRE-006] Structured logging outputs human-readable console format instead of JSON

zerolog is configured with ConsoleWriter (human text) instead of JSON output — incompatible with log aggregators like Datadog/Loki/ELK that expect JSON.

**Evidence:**
```
API log output shows colored text like 2024-01-01 00:00:00 INF ... instead of {"level":"info",...}
```

**File:** internal/config/config.go:~1
**Agent:** SRE-006