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).

docs/OVERVIEW.md

@@ -310,13 +310,10 @@ per model and one agent per subagent the `task` tool spawned (its journal sits i
 the folder named like the session's). An omp session can be resumed by id from
 its workspace (`omp --resume <id>`), like a Claude or Codex one.
 
-**OpenCode** sessions are read from its SQLite store
-(`~/.local/share/opencode/opencode.db`, every `DASHBOARD_OPENCODE_POLL_MS` ms),
-with their tokens and cost per model and one agent per subagent, and are
-resumable by id (`opencode --session <id>`). **Grok Build** runs the Claude hooks in
-`~/.claude/settings.json` itself, so its sessions arrive through AgentHub's own
-hooks, recorded as Grok sessions (live status, no tokens); they resume with
-`grok --resume <id>`. Cursor sessions resume by id too (`--resume <id>`).
+Cursor sessions resume by id too (`--resume <id>`), and open as a chat like
+omp ones. OpenCode and Grok Build are no longer AgentHub tools: a Grok Build
+running the Claude hooks in `~/.claude/settings.json` is ignored, and sessions an
+older build recorded for either stay in the history.
 
 **Pipelines are dormant.** AgentHub ships no pipeline template, so a workspace has no
 stages until you drop a template JSON into `DASHBOARD_PIPELINES_DIR` (see