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/db.js

@@ -1486,23 +1486,6 @@ db.exec(`
   CREATE INDEX IF NOT EXISTS idx_omp_sessions_session ON omp_sessions(session_id);
 `);
 
-// Which OpenCode stores have been read at what mtime, and per root session the
-// newest `time_updated` written (server/lib/opencode-usage.js) — the same
-// "deleted stays deleted" rule.
-db.exec(`
-  CREATE TABLE IF NOT EXISTS opencode_stores (
-    path TEXT PRIMARY KEY,
-    mtime_ms INTEGER NOT NULL DEFAULT 0,
-    updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
-  );
-  CREATE TABLE IF NOT EXISTS opencode_sessions (
-    session_id TEXT PRIMARY KEY,
-    store TEXT NOT NULL,
-    time_updated INTEGER NOT NULL DEFAULT 0,
-    updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
-  );
-`);
-
 // Which Cursor agent transcripts have been read, at what mtime
 // (server/lib/cursor-usage.js) — the same "deleted stays deleted" rule.
 db.exec(`