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/api/src/lib/feature-status.ts

@@ -55,14 +55,14 @@ export function ensureAiDirs(): void {
     mkdirSync(MODELS_DIR, { recursive: true });
     mkdirSync(join(AI_DIR, "pip-cache"), { recursive: true });
   } catch (err: unknown) {
+    // Never refuse to boot over the AI data dir. On native checkouts the
+    // default DATA_DIR (/data) is often uncreatable (ENOENT/EROFS on a
+    // sealed macOS root, EACCES on restrictive volumes); AI tools simply
+    // report as not installed until DATA_DIR points somewhere writable.
     const code = (err as NodeJS.ErrnoException).code;
-    if (code === "EACCES") {
-      console.error(
-        `WARNING: Cannot create AI directories under "${AI_DIR}". AI features will be unavailable. Check volume permissions (PUID/PGID).`,
-      );
-      return;
-    }
-    throw err;
+    console.error(
+      `WARNING: Cannot create AI directories under "${AI_DIR}" (${code}). AI features will be unavailable. Set DATA_DIR to a writable path (or check volume permissions / PUID / PGID in Docker).`,
+    );
   }
 }