v0.3.1 — quieter cold-start logs

Fix

Cold-start with HTTP-only blocklist sources no longer emits a spurious WARN. When every configured source is type: http and the on-disk cache is empty (first run, or no volume mounted), the matcher is empty by design — the fetcher populates it within a few seconds. Previously the startup log line was:

```
WARN blocklist sources configured but yielded zero entries — check paths and file contents
```

which falsely implied operator misconfiguration. The expected case now logs at INFO:

```
INFO blocklist cache cold — fetcher will populate; block stage is a no-op until first fetch lands
```

The original WARN still fires for genuine misconfiguration (file source pointing at an empty/missing path, or mixed sources where the file half yields nothing).

Upgrade

Drop-in. No config changes. No behavioural change beyond the startup log line.

```
docker pull ghcr.io/bcrisp4/bns:0.3.1
```