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/configuration.md

@@ -359,8 +359,8 @@ Skills can declare their own configuration settings via their SKILL.md frontmatt
 ```yaml
 skills:
   config:
-    wiki:
-      path: ~/wiki          # Used by the llm-wiki skill
+    myplugin:
+      path: ~/myplugin-data   # Example — each skill defines its own keys
 ```
 
 **How skill settings work:**
@@ -372,7 +372,7 @@ skills:
 **Setting values manually:**
 
 ```bash
-hermes config set skills.config.wiki.path ~/my-research-wiki
+hermes config set skills.config.myplugin.path ~/myplugin-data
 ```
 
 For details on declaring config settings in your own skills, see [Creating Skills — Config Settings](/docs/developer-guide/creating-skills#config-settings-configyaml).