Fix Hermes plugin config: use config file instead of env vars

Hermes plugins don't inherit container env vars. Switch the Miniflux
plugin to read credentials from a config.json written by Ansible,
and drop requires_env / container env vars.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/hermes/plugins/miniflux/plugin.yaml

@@ -1,10 +1,6 @@
 name: miniflux
 version: 1.0.0
 description: Read feeds and entries from the local Miniflux RSS reader
-requires_env:
-  MINIFLUX_API_KEY:
-    description: Miniflux API key (generate in Miniflux → Settings → API Keys)
-    secret: true
 provides_tools:
   - list_feeds
   - get_unread_entries