refactor: lightweight hermes-agent skill as doc navigation index

Reduce SKILL.md from ~1020 lines (46KB) to 90 lines by replacing
duplicated CLI reference, config tables, troubleshooting, and
contributor guides with a local-first navigation index pointing
to website/docs/.

Pitfalls moved into their proper docs:
- configuring-models.md: fixed misleading 'auto' resolution (main
  provider first, not OpenRouter), added context_length global vs
  per-model, max_tokens ceiling, and OpenRouter cache defaults
- adding-tools.md: new 'After Adding: Restart Required' section
- cron-troubleshooting.md: import errors + lazy import definitive fix

The skill retains the full What Makes Hermes Different descriptions
and Key Rules (prompt caching, role alternation, paths, config vs
env, check_fn, fabrication) that guide agent behavior.

Follows the pattern from PR #4414 (SKILL.md + references/) and
addresses the context budget concern in issue #10666.

website/docs/developer-guide/adding-tools.md

@@ -200,6 +200,28 @@ OPTIONAL_ENV_VARS = {
 }
 ```
 
+## After Adding: Restart Required
+
+New tools are discovered at process startup. Slash commands like `/reset` and `/new` only reset the conversation thread — they do **not** reload the tool palette. For a new tool to become available:
+
+```bash
+hermes gateway stop && hermes gateway start
+```
+
+**Do NOT use `hermes gateway run --replace`** — it can leave stale Python import state that causes the new process to inherit the old tool palette. Always use `stop` + `start` when registering new tools.
+
+To verify the tool is properly registered before restarting:
+
+```bash
+cd ~/.hermes/hermes-agent
+source venv/bin/activate
+python3 -c "
+from tools.registry import registry, discover_builtin_tools
+loaded = discover_builtin_tools()
+print('Registered:', 'your_tool_name' in registry.get_all_tool_names())
+"
+```
+
 ## Checklist
 
 - [ ] Tool file created with handler, schema, check function, and registration