fix(upgrade): re-run install.sh instead of installing the wrong npm package

`agent-browser-stealth upgrade` (inherited from upstream) queried
registry.npmjs.org/agent-browser and ran `npm/pnpm install -g
agent-browser@latest` — installing the UNRELATED upstream `agent-browser`
package and clobbering the user's stealth install (reported in testing).

The stealth fork ships via GitHub Releases, so `upgrade` now just re-runs
install.sh into the same directory as the current binary — identical to the
install path, always tracking the freshest Release. (Windows prints manual
download instructions.)

Also bump CI actions off the deprecated Node 20 runtime (GitHub forces Node 24
on 2026-06-16): checkout v4->v6, upload-artifact v4->v7, download-artifact
v4->v8, action-gh-release v2->v3.

.github/workflows/release-binaries.yml

@@ -36,7 +36,7 @@ jobs:
           - { name: macOS ARM64,      os: macos-latest,  target: aarch64-apple-darwin,        asset: agent-browser-darwin-arm64,     use_zigbuild: false, ext: '' }
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.event.inputs.tag || github.ref }}
 
@@ -102,7 +102,7 @@ jobs:
           )
 
       - name: Upload artifact
-        uses: actions/upload-artifact@v4
+        uses: actions/upload-artifact@v7
         with:
           name: ${{ matrix.asset }}
           path: dist/${{ matrix.asset }}.tar.gz*
@@ -117,7 +117,7 @@ jobs:
       contents: write
     steps:
       - name: Download all artifacts
-        uses: actions/download-artifact@v4
+        uses: actions/download-artifact@v8
         with:
           path: dist
           merge-multiple: true
@@ -126,7 +126,7 @@ jobs:
         run: ls -la dist
 
       - name: Attach to release
-        uses: softprops/action-gh-release@v2
+        uses: softprops/action-gh-release@v3
         with:
           tag_name: ${{ github.event.inputs.tag || github.ref_name }}
           files: |