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/src/lib/tool-display-modes.ts

@@ -0,0 +1,91 @@
+/**
+ * Pure display-mode map: toolId -> DisplayMode.
+ *
+ * This module intentionally has no React imports so that Playwright specs and
+ * Node-side test generators can import it directly. It is the single source of
+ * truth for display modes; tool-registry.tsx merges it into registry entries.
+ */
+
+export type DisplayMode =
+  | "side-by-side"
+  | "before-after"
+  | "live-preview"
+  | "no-comparison"
+  | "interactive-crop"
+  | "interactive-eraser"
+  | "interactive-split"
+  | "no-dropzone"
+  | "custom-results";
+
+export const TOOL_DISPLAY_MODES: Record<string, DisplayMode> = {
+  // Essentials
+  resize: "side-by-side",
+  crop: "interactive-crop",
+  rotate: "side-by-side",
+  convert: "no-comparison",
+  compress: "before-after",
+  "strip-metadata": "no-comparison",
+  "edit-metadata": "no-comparison",
+
+  // Color adjustments
+  "adjust-colors": "live-preview",
+  sharpening: "before-after",
+
+  // Watermark & overlay
+  "watermark-text": "before-after",
+  "watermark-image": "before-after",
+  "text-overlay": "before-after",
+  compose: "before-after",
+  "meme-generator": "no-dropzone",
+
+  // Utilities
+  info: "no-comparison",
+  compare: "before-after",
+  "find-duplicates": "custom-results",
+  "color-palette": "no-comparison",
+  "qr-generate": "no-dropzone",
+  "html-to-image": "no-dropzone",
+  "barcode-read": "before-after",
+  "image-to-base64": "custom-results",
+
+  // Layout & composition
+  collage: "no-dropzone",
+  stitch: "no-comparison",
+  split: "interactive-split",
+  border: "live-preview",
+  beautify: "live-preview",
+
+  // Format & conversion
+  "svg-to-raster": "before-after",
+  vectorize: "before-after",
+  "gif-tools": "before-after",
+
+  // Optimization extras
+  "bulk-rename": "before-after",
+  favicon: "before-after",
+  "image-to-pdf": "before-after",
+  "optimize-for-web": "before-after",
+  "pdf-to-image": "no-dropzone",
+
+  // Adjustments extra
+  "replace-color": "before-after",
+  "color-blindness": "before-after",
+
+  // AI tools
+  "remove-background": "before-after",
+  upscale: "before-after",
+  ocr: "before-after",
+  "blur-faces": "before-after",
+  "enhance-faces": "before-after",
+  "erase-object": "interactive-eraser",
+  "smart-crop": "before-after",
+  "image-enhancement": "before-after",
+  colorize: "before-after",
+  "noise-removal": "before-after",
+  "passport-photo": "custom-results",
+  "red-eye-removal": "before-after",
+  "restore-photo": "before-after",
+  "transparency-fixer": "before-after",
+  "content-aware-resize": "side-by-side",
+  "ai-canvas-expand": "before-after",
+};