fix: stop hermes update from nagging about llm-wiki's wiki.path (#11222)

llm-wiki was the only shipped skill using metadata.hermes.config, which
caused 'hermes update' and 'hermes config migrate' to prompt for a wiki
directory on every run — even for users who have never touched the skill
— because 'enabled' is opt-out (all shipped skills count as enabled unless
explicitly disabled). Declining the prompt didn't persist anything, so
the nag fired again on every update.

Switch llm-wiki to the env var + runtime default pattern that obsidian and
google-workspace already use: WIKI_PATH env var, default $HOME/wiki. No
prompting infrastructure, no config.yaml touch, no nag loop.

Changes:
- skills/research/llm-wiki/SKILL.md: remove metadata.hermes.config,
  document WIKI_PATH env var in the Wiki Location section, update the
  orientation snippet and initialization guidance.
- Docs: replace llm-wiki's wiki.path examples with a generic 'myplugin.path'
  placeholder across configuration.md, features/skills.md, and
  creating-skills.md so users don't try to set skills.config.wiki.path
  expecting llm-wiki to use it.
- skills-catalog.md: mention WIKI_PATH instead of skills.config.wiki.path.

E2E verified: discover_all_skill_config_vars() and get_missing_skill_config_vars()
both return 0 entries after this change, so the prompt branch in migrate_config()
no longer fires.

The metadata.hermes.config feature stays in place for third-party skills
that genuinely need structured config, but built-ins now prefer env vars.

website/docs/user-guide/features/skills.md

@@ -155,10 +155,10 @@ Skills can also declare non-secret config settings (paths, preferences) stored i
 metadata:
   hermes:
     config:
-      - key: wiki.path
-        description: Path to the wiki directory
-        default: "~/wiki"
-        prompt: Wiki directory path
+      - key: myplugin.path
+        description: Path to the plugin data directory
+        default: "~/myplugin-data"
+        prompt: Plugin data directory path
 ```
 
 Settings are stored under `skills.config` in your config.yaml. `hermes config migrate` prompts for unconfigured settings, and `hermes config show` displays them. When a skill loads, its resolved config values are injected into the context so the agent knows the configured values automatically.