fix(tooling): restore L0 coverage sweep across all packages

The template baseline shipped 9 packages without @vitest/coverage-v8
and documented an L0 invocation turbo cannot parse — the full coverage
sweep had never run. Adds the provider (pinned to the feature-package
spec), a root test:coverage script, corrects every live doc/prompt/CI
occurrence, and calibrates coverage excludes for the 4 packages whose
latent threshold failures the outage masked (framework glue only —
zero threshold numbers changed). L0 sweep now passes 21/21.

Squash of a284baa + 5c6af95 (worktree-agent-a013c67cea83b2636),
implemented and reviewed via the dispatch loop under the epic's
baseline waiver (lint pending story 03).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

apps/web-next/vitest.config.ts

@@ -2,7 +2,25 @@ import path from "node:path";
 import { mergeConfig } from "vitest/config";
 import { jsdomVitestConfig } from "@repo/core-typescript/vitest.base.jsdom";
 
+// Coverage excludes mirror the feature-package pattern (see
+// packages/auth/vitest.config.ts): framework glue is excluded, thresholds
+// stay inherited from the shared base — never lowered here.
 export default mergeConfig(jsdomVitestConfig, {
   esbuild: { jsx: "automatic" },
+  test: {
+    coverage: {
+      exclude: [
+        // Next.js App Router entry points — async server components and the
+        // tRPC route-handler mount, invoked by the framework and covered by
+        // Playwright e2e; not unit-testable in jsdom. providers.tsx and
+        // src/server/** stay counted (they have unit tests).
+        "src/app/**/layout.tsx",
+        "src/app/**/page.tsx",
+        "src/app/**/route.ts",
+        // Ambient type declarations — no executable code
+        "src/**/*.d.ts",
+      ],
+    },
+  },
   resolve: { alias: { "@": path.resolve(__dirname, "./src") } },
 });