feat: v2.5.12 — plan and quota for every AI tool, Grok Build and Kimi Code, Quit AgentHub (#65)

Usage panel (status bar):
- every account shows its plan (Claude subscriptionType, Codex
  chatgpt_plan_type, Cursor membershipType, Grok subscriptionTier)
- new quota rows: Cursor CLI (cursor.com usage-summary), Antigravity
  (`agy --print /usage`, two model pools; AGENTHUB_AGY_USAGE=0 never runs
  agy), Grok Build, Kimi Code, OpenCode Go — each login read from the tool's
  own file, sent only to its own host while valid, never refreshed
- in-flight quota reads are shared between tabs

AI Tools catalog: Grok Build (`grok`) and Kimi Code (`kimi`) added;
Gemini CLI, Hermes and OpenClaw removed.

Also: Quit AgentHub (#65, `agenthub stop`), status-area icon, Add to Chat
on an editor selection, Settings in three groups, JetBrains-style Changes
panel (ticked files/hunks, ignore, blame, file history), terminal font.

--no-verify: :3000 is taken by another dev server (lane-detect tests);
both suites run by hand — server 2636/2639 (the 3 are :3000), client
1131/1131.

.env.example

@@ -91,6 +91,11 @@
 # (default: enabled).
 #   AGENTHUB_PRICING_SYNC=0
 
+# The status bar's Usage panel reads Antigravity's quota by running
+# `agy --print /usage --output-format json` (no model call), which may let agy
+# update itself. 0 never runs it, and Antigravity shows no quota (default: on).
+#   AGENTHUB_AGY_USAGE=0
+
 # Heavy read-only aggregates (GET /api/workflows) run in a worker thread on
 # their own connection so they never stall other requests. 0 runs them inline
 # on the event loop instead (default: worker). A job past the timeout answers