feat: per-tool settings, persistent settings file, Codex and Antigravity sessions, tokens and hooks (#40 B, C1, C2, D)

Part B: Model Pricing, Hook Configuration and CLAUDE_HOME move from
Settings → Dashboard to the Claude Code tab's AgentHub sub-tab
(ClaudeAgentHubSettings.tsx); CODEX_HOME is editable in Codex → AgentHub.
A home that is or contains the OS home is refused (EBADHOME).

Settings persistence: dashboard-saved settings go to
~/.config/agenthub/settings.env (AGENTHUB_SETTINGS_FILE), outside the plugin
cache an update wipes. Load order: real env > the checkout's .env > that file.
The first CLAUDE_HOME change pins DASHBOARD_DATA_DIR so the DB stays put.

C1: codex-usage.js reads Codex rollout journals into sessions (new column
tool) and token_usage, tracked per file in codex_rollouts; forks deduped by
total vector, sub-agent threads folded into the root; pricing-sync also
prices OpenAI models; PricingSettings with a vendor filter.

C2: codex-hooks.js installs AgentHub's hooks into $CODEX_HOME/hooks.json on
a click, through a stable forwarder; Codex trust is never written. The hook
route creates tool='codex' sessions and folds sub-agent hooks into the root.

D: antigravity-usage.js reads agy's per-conversation SQLite files (tokens
from ModelUsageStats) into tool='antigravity' sessions; antigravity-hooks.js
installs the named hook `agenthub` (PreInvocation, PostToolUse, Stop — never
PreToolUse) into ~/.gemini/config/hooks.json; Settings → Antigravity tab;
Gemini pricing.

Whole-change review fixes: sameOriginGuard on both home PUTs, routers.missing
on a CLAUDE_HOME change, reset-pricing scope, GET /api/sessions?tool=,
clear-data covering the new tables, Codex child-thread events moving no
status, hooks owning status only while current, EFOREIGN for a forwarder
that is not ours, agy quiet window and turn rules, AGENTHUB_SETTINGS_FILE
honoured from .env.

Docs, OpenAPI and the CLAUDE.md marker updated. Server 2141, client 779.

client/src/pages/SettingsHub.tsx

@@ -1,16 +1,24 @@
 /**
  * @file SettingsHub.tsx
- * @description Tabbed shell for /settings that hosts the dashboard's own settings plus one configuration panel per AI tool (Claude Code and Codex) plus the AI Router profiles they can be pointed at and the git logins dashboard fetch/pull/push use, with the active tab kept in the `?tool=` query param. A tool's tab is hidden while that tool is disabled in Settings → AI Tools.
+ * @description Tabbed shell for /settings that hosts the dashboard's own settings plus one configuration panel per AI tool (Claude Code, Codex and Antigravity) plus the AI Router profiles they can be pointed at and the git logins dashboard fetch/pull/push use, with the active tab kept in the `?tool=` query param. A tool's tab is hidden while that tool is disabled in Settings → AI Tools.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 import type { ComponentType } from "react";
 import { useSearchParams } from "react-router-dom";
 import { useTranslation } from "react-i18next";
-import { Boxes, KeyRound, Router, Settings as SettingsIcon, SquareTerminal } from "lucide-react";
+import {
+  Boxes,
+  KeyRound,
+  Orbit,
+  Router,
+  Settings as SettingsIcon,
+  SquareTerminal,
+} from "lucide-react";
 import { PageTabs } from "../components/PageTabs";
 import { Settings } from "./Settings";
 import { CcConfig } from "./CcConfig";
 import { CodexConfig } from "./CodexConfig";
+import { AntigravityConfig } from "./AntigravityConfig";
 import { AiRouterConfig } from "./AiRouterConfig";
 import { GitCredentialsConfig } from "./GitCredentialsConfig";
 import { useAiTools } from "../hooks/useAiTools";
@@ -48,6 +56,13 @@ const TOOL_TABS: ToolTab[] = [
     Panel: CodexConfig,
     aiTool: "codex",
   },
+  {
+    id: "antigravity",
+    labelKey: "tools.antigravity",
+    Icon: Orbit,
+    Panel: AntigravityConfig,
+    aiTool: "antigravity",
+  },
   { id: "ai-router", labelKey: "tools.aiRouter", Icon: Router, Panel: AiRouterConfig },
   {
     id: "git-credentials",