perf(dashboard): server-prefetch the snapshot into the first HTML + bundle budget gate

The measured first-load gap on / was never the server: FCP painted the
SSR shell at ~1.8 s but LCP landed at ~5.5 s (mobile-throttled) because
the tiles waited for JS download + hydrate + a CLIENT-side snapshot
fetch — while /api/dashboard/snapshot answers in ~8 ms server-side.

src/app/page.tsx is now a thin RSC wrapper: it runs the same cached
snapshot read the API route uses (extracted to
src/lib/dashboard/snapshot-read.ts, one shared SWR cell for both
readers) and hands the result to TanStack via HydrationBoundary +
dehydrate, so the first HTML carries real tile data and the mounted
cell starts warm (staleTime 60 s, refetchOnMount false — no double
fetch). Query keys come only from the central factory
(dashboardSnapshot(locale) + the dashboardWidgets seed the client cell
already performs); the payload is JSON-round-tripped so the hydrated
shape is byte-equal to the wire shape. Fail-soft: no session or any
builder error renders the page exactly as before. The 1,727-line client
page moves unchanged to src/app/page-client.tsx; no component-tree
rewrite.

Companion: the documented bundle tooling was dead on Turbopack
(ANALYZE=1 silent no-op, bundle-report read a webpack-only JSON), so
H2/H3-class regressions shipped invisibly. scripts/check-bundle-budget.mjs
derives per-route gzip totals from the Turbopack client-reference
manifests + rootMainFiles, prints the report (pnpm bundle-report), and
enforces bundle-budget.json (pnpm bundle-check): per-route caps,
total-client-JS cap, a recharts-duplication guard (fingerprint count
must stay 1), and a catalog guard (no message catalog referenced by any
route manifest). Wired into the existing e2e workflow after next build.

H4

package.json

@@ -29,7 +29,8 @@
     "prebuild": "node scripts/generate-sw-version.mjs",
     "build": "next build",
     "analyze": "ANALYZE=1 next build",
-    "bundle-report": "node scripts/print-bundle-report.mjs",
+    "bundle-report": "node scripts/check-bundle-budget.mjs",
+    "bundle-check": "node scripts/check-bundle-budget.mjs --check",
     "start": "next start",
     "lint": "eslint",
     "db:generate": "prisma generate",