remove: BOOT.md built-in hook (#17093)

BOOT.md was merged in PR #3733 before the feature was ready — the
built-in hook spawned a bare AIAgent() with no model/runtime kwargs,
which immediately 401s on any provider with a custom endpoint. Three
separate community PRs (#5240, #12514, #14992) tried to paper over it.

Remove the BOOT.md hook entirely and its user-facing docs/tips. Keep
the gateway/builtin_hooks/ package and the HookRegistry._register_builtin_hooks()
hook-point intact as the extension surface for future always-on
gateway hooks.

Closes #5239.

Co-authored-by: teknium1 <teknium@users.noreply.github.com>

hermes_cli/tips.py

@@ -263,7 +263,6 @@ TIPS = [
     "hermes status --deep runs deeper diagnostic checks across all components.",
 
     # --- Hidden Gems & Power-User Tricks ---
-    "BOOT.md at ~/.hermes/BOOT.md runs automatically on every gateway start — use it for startup checks.",
     "Cron jobs can attach a Python script (--script) whose stdout is injected into the prompt as context.",
     "Cron scripts live in ~/.hermes/scripts/ and run before the agent — perfect for data collection pipelines.",
     "prefill_messages_file in config.yaml injects few-shot examples into every API call, never saved to history.",