chore: bump Playwright to 1.64.1 and unpin the browser suite

Playwright supports Ubuntu 26.04 from 1.61.0, so the browser suite can go
back to ubuntu-latest. Raises the floor in package.json as well, because
the old ^1.58.0 still admitted versions that refuse to install on the
image every workflow now runs on. Bundled Chromium moves from 148 to 156.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

package.json

@@ -133,7 +133,7 @@
     "exceljs": "4.4.0",
     "fflate": "0.8.3",
     "pixelmatch": "^6.0.0",
-    "playwright": "^1.58.0",
+    "playwright": "^1.64.1",
     "pngjs": "^7.0.0",
     "postcss": "^8.5.15",
     "prettier": "^3.4.0",