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__/ai-tool-config.test.js

@@ -45,7 +45,7 @@ before(async () => {
     builtin,
     tool("gem", [
       { path: "~/.gem/settings.json" },
-      { path: "~/.gem/opencode.jsonc" },
+      { path: "~/.gem/tool.jsonc" },
       { path: "~/.gem/GEMINI.md" },
       { path: "~/.gem/missing.json" },
     ])
@@ -57,7 +57,7 @@ before(async () => {
 
   fs.mkdirSync(path.join(home, ".gem"));
   fs.writeFileSync(path.join(home, ".gem/settings.json"), '{"theme":"dark"}\n', { mode: 0o600 });
-  fs.writeFileSync(path.join(home, ".gem/opencode.jsonc"), '{\n  // c\n  "a": 1,\n}\n');
+  fs.writeFileSync(path.join(home, ".gem/tool.jsonc"), '{\n  // c\n  "a": 1,\n}\n');
   fs.writeFileSync(path.join(home, ".gem/GEMINI.md"), "# rules\n");
 
   const express = require("express");