ci: run e2e on Node 24 and cache the Electron binary

The Linux e2e job kept failing with 'Electron failed to install correctly'
even after an explicit install.js step. Move the runner from Node 26 (Current,
three weeks old) to Node 24 (active LTS) so Electron's install tooling and
Playwright run on the stable line, and cache ~/.cache/electron so launch does
not depend on a fresh binary fetch each run.

Note: AI-assisted (Claude Code). Manually verified: prettier clean; the
actions/cache pin is the real v4.3.0 SHA.

Author: notluquis

.github/workflows/e2e.yml

@@ -21,12 +21,21 @@ jobs:
       - uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
       - uses: actions/setup-node@a0853c24544627f65ddf259abe73b1d18a591444 # v5
         with:
-          node-version: '26.x'
+          # Node 24 (active LTS), not 26 (Current): keep the e2e runner on the
+          # stable line for Electron's install tooling and Playwright.
+          node-version: '24.x'
           cache: 'yarn'
+      # Cache the @electron/get binary download so launch does not depend on a
+      # fresh GitHub-releases fetch every run.
+      - uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+        with:
+          path: ~/.cache/electron
+          key: ${{ runner.os }}-electron-${{ hashFiles('yarn.lock') }}
+          restore-keys: ${{ runner.os }}-electron-
       - run: yarn install --frozen-lockfile
-      # Ensure Electron's platform binary is present; its postinstall can be
-      # skipped when node_modules is restored from cache, which fails launch
-      # with "Electron failed to install correctly".
+      # Materialize Electron's platform binary into node_modules/electron/dist;
+      # its postinstall can be skipped on a cache-restored tree, which fails
+      # launch with "Electron failed to install correctly".
       - run: node node_modules/electron/install.js
       - run: yarn build
       # Electron needs system libraries; xvfb provides a display on the headless