Add desktop/server MP4 export pipeline, hardening, and render tests (v1.3.0)

Desktop MP4 export renders frames from a hidden BrowserWindow via
capturePage, pipes PNGs to a bundled ffmpeg (libx264/yuv420p/+faststart),
and writes the file through an atomic temp-file swap. It shares scene
validation (shared/renderValidation.cjs) and the render.html renderer with
the standalone Puppeteer server, which is hardened in parallel.

Render worker & main (electron/):
- abortable render loop with an inactivity watchdog and cancel plumbing
- atomic temp-file + rename so a cancel/failure never truncates a
  pre-existing target (#7); stdin EPIPE / early-exit / backpressure-hang
  handled (#8)
- HiDPI frames normalized to canvas size (#10); odd dimensions padded to
  even (#13, also server); backgroundThrottling disabled (#12)
- reject canvases larger than the display (#11); single-render guard;
  isolated render session that blocks network requests (#5)

Tests:
- Electron harnesses (scripts/verify-*.cjs) for capture, export, cancel,
  timeout, assets, background, capture-fidelity, resolution, odd-dims,
  aggregated by verify-desktop-render.cjs
- server smoke + e2e and shared validation unit tests
- headless hook (src/devtools/headless.ts) to run the in-app suite under
  browser/electron hosts; pixel-diff util + capture fixtures (test/)
- dev_docs plans: integration, fixes (#7-#13), and the e2e/capture strategy

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "ruwio",
   "private": true,
-  "version": "1.2.15",
+  "version": "1.3.0",
   "type": "module",
   "main": "dist-electron/main.cjs",
   "scripts": {
@@ -9,11 +9,17 @@
     "build": "vue-tsc --noEmit && vite build",
     "desktop:dev": "concurrently -k \"vite\" \"wait-on http://localhost:5200 && npm run desktop:start\"",
     "desktop:start": "tsc -p tsconfig.electron.json && electron .",
-    "desktop:build": "npm run build && tsc -p tsconfig.electron.json && electron-builder",
-    "desktop:pack": "npm run build && tsc -p tsconfig.electron.json && electron-builder --dir",
+    "desktop:build": "npm run build && tsc -p tsconfig.electron.json && npm run stage:ffmpeg -- --optional && electron-builder",
+    "desktop:pack": "npm run build && tsc -p tsconfig.electron.json && npm run stage:ffmpeg -- --optional && electron-builder --dir",
     "preview": "vite preview",
     "type-check": "vue-tsc --noEmit",
-    "pack": "bash scripts/pack.sh"
+    "pack": "bash scripts/pack.sh",
+    "test:render-validation": "node --test shared/renderValidation.test.cjs",
+    "test:render-server": "node --test server/server.smoke.test.cjs",
+    "test:render-server:e2e": "node --test server/render.e2e.test.cjs",
+    "test:render-desktop": "tsc -p tsconfig.electron.json && node scripts/verify-desktop-render.cjs",
+    "test:capture-fidelity": "tsc -p tsconfig.electron.json && electron scripts/verify-capture-fidelity.cjs",
+    "stage:ffmpeg": "node scripts/stage-ffmpeg.cjs"
   },
   "dependencies": {
     "@phosphor-icons/vue": "^2.2.1",
@@ -39,18 +45,31 @@
     "appId": "app.ruwio.desktop",
     "productName": "RUWIO",
     "icon": "icon.png",
+    "npmRebuild": false,
     "directories": {
       "output": "release"
     },
     "files": [
       "dist/**/*",
       "dist-electron/**/*",
+      "shared/renderValidation.cjs",
       "package.json"
     ],
     "extraResources": [
       {
         "from": "build/icon.png",
         "to": "build/icon.png"
+      },
+      {
+        "from": "server/render.html",
+        "to": "server/render.html"
+      },
+      {
+        "from": "bin",
+        "to": "bin",
+        "filter": [
+          "**/*"
+        ]
       }
     ],
     "linux": {