test: testing overhaul -- CI e2e gates, parallel suites, generated matrices, mutation testing (#215)

Closes the "e2e never runs in CI" hole. Adds per-PR e2e smoke gate,
nightly full-suite workflows, parallel vitest forks (per-fork DBs),
Playwright parallel/serial/visual projects against production builds,
metadata-generated test suites (drift guards, hostile inputs, format
matrix, pairwise settings, property-based fuzz), Stryker mutation
testing, Schemathesis API fuzz, coverage ratchet, and fixes for three
session-poisoning bugs that caused 200+ serial-bucket failures.

Bug fix included: favicon/split/bulk-rename could hang clients forever
when ZIP streaming failed after reply.hijack().

apps/web/vite.config.ts

@@ -22,6 +22,19 @@ export default defineConfig({
       },
     },
   },
+  // vite preview serves the production build for e2e runs; it needs the same
+  // /api proxy the dev server has (the app always calls relative /api).
+  preview: {
+    host: true,
+    port: Number(process.env.PORT) || 1351,
+    proxy: {
+      "/api": {
+        target: process.env.VITE_API_URL || "http://localhost:13490",
+        timeout: 300_000,
+        proxyTimeout: 300_000,
+      },
+    },
+  },
   build: {
     rollupOptions: {},
   },