feat(ai-tools): drop OpenCode and Grok Build

- opencode.json / grok.json leave the built-in catalog; opencode-usage.js,
  its poller, transcript branch and table creation go with it (existing
  tables and session rows stay as history).
- A Grok payload reaching the Claude hook route (Grok runs the Claude hooks
  itself) is dropped instead of recorded as tool = 'grok'.
- quota.js no longer reads Grok or OpenCode Go logins.
- Redone on v2.8.22 from c6b2892 (feat/grok-usage, never merged).

server/__tests__/fixtures/ai-tools/septool.json

@@ -0,0 +1,10 @@
+{
+  "id": "septool",
+  "label": "Separator tool",
+  "detect": ["septool"],
+  "prompt": {
+    "mode": "argv",
+    "separator": "--"
+  },
+  "bypass": ["--permission-mode", "bypassPermissions"]
+}