feat: analytics parity — tool cost, date ranges, budgets, query explorer, replay, snapshots (v2.4.0)

Analytics parity phases 2–7 (docs/plans/analytics-parity/), built on
138e706 and ported onto v2.3.1:
- Cost by AI tool (?tool= on cost/analytics/stats/workflows, by_tool,
  Codex fast/priority and flex tiers, agenthub_cost_usd_total{tool,model})
- Date ranges (from/to) on cost/analytics/workflows; Analytics range select
  with Today / This week (Monday) / This month (1st) / 7d / 30d / 90d / All /
  Custom; workflow filters carried into workflow-stats.js (read worker)
- Budgets and cost alerts as alert rule types (alert_rules rebuilt without
  its rule_type CHECK), GET /api/budgets/status, rule preview, spend pace,
  status-bar budget chip; rules stay editable in place
- Query Explorer (/query, allowlisted sort, CSV/JSON export) and scheduled
  reports (report_definitions/report_runs, Settings → Reports)
- Session Replay tab and immutable snapshots (session_snapshots, /snapshot/:token)
- Remote Codex sync, push ingest with a hashed token, privacy redaction and
  ignored folders (Settings → Data), Cursor sessions (no cost)
- Read-only MCP server, statusline, Grafana/Prometheus files

Also: resizable sidebar, pet run/wave animations, the workspace home keeps a
half-typed prompt, and the pre-commit hook runs only the related tests for a
small commit.

server/routes/budgets.js

@@ -0,0 +1,20 @@
+/**
+ * @file Express router for spend budgets. A budget is an alert rule of type
+ * `budget` (created, edited and deleted through /api/alerts/rules); this router
+ * only reads: `GET /api/budgets/status` lists every enabled budget with its
+ * current-period spend, percent of the limit, projected end-of-period spend and
+ * the thresholds reached (server/lib/budgets.js).
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+const { Router } = require("express");
+const { budgetStatus } = require("../lib/budgets");
+
+const router = Router();
+
+// GET /api/budgets/status
+router.get("/status", (_req, res) => {
+  res.json({ budgets: budgetStatus() });
+});
+
+module.exports = router;