Fix Linux About dialog icon handling

[lw33]

What changed

On Linux the About dialog showed no icon, or could crash with an uncaught promise rejection. This PR wires up a proper bundled icon path for Linux and adds null-safety guards on the icon return values so the dialog renders correctly regardless of which code path is taken.

Why it changed

The upstream About-dialog helper (bZ in the minified main bundle) unconditionally calls app.getFileIcon and then calls .isEmpty() on the result without guarding against null. On Linux:

1. app.getFileIcon can reject on some desktop environments, leaving the icon promise unresolved or throwing.
2. The windowIcon field propagated downstream without a null check, so d.windowIcon.isEmpty() threw when the icon was null.
3. No bundled Linux asset was ever supplied to the dialog — the function only tried macOS thumbnail (Fw) or the system file-icon API, both of which are no-ops or failures on Linux.

The patch (applyLinuxAboutDialogPatch) addresses all three:

• On Linux it short-circuits the macOS-only Fw call to null.
• It replaces the app.getFileIcon call with nativeImage.createFromPath(iconPathExpression) pointing at the bundled content/webview/assets/app-test.png asset, wrapped in an IIFE that returns null on an empty image instead of propagating an empty NativeImage.
• It guards i.isEmpty() → i==null||i.isEmpty() and d.windowIcon.isEmpty() → d.windowIcon==null||d.windowIcon.isEmpty() and windowIcon:i} → windowIcon:i??null} throughout the downstream spread.
• getFileIcon on non-Linux paths gets .catch(()=>null) so a rejection no longer propagates.

The patch is ciPolicy: "optional" (fail-soft): if the minified bundle changes shape the dialog silently falls back to its previous behavior rather than breaking startup.

Source-of-truth files changed

• scripts/patches/main-process.js — new applyLinuxAboutDialogPatch function
• scripts/patches/core/all-linux/main-process/window-shell/patch.js — registers the patch descriptor (id: "linux-about-dialog", phase main-bundle, order 55)
• scripts/patch-linux-window-ui.js — imports and re-exports applyLinuxAboutDialogPatch
• scripts/patch-linux-window-ui.test.js — adds the patch to the uniqueness registry test and adds a focused unit test covering the icon-path substitution, null-safe guards, and idempotency

Validation

node scripts/patch-linux-window-ui.test.js

All tests pass, including the new "makes About dialog prefer the bundled Linux icon asset" case. The test covers:

• nativeImage.createFromPath(...) substitution present in patched output
• process.platform===\linux`?null:...` short-circuit for the macOS thumbnail call
• windowIcon==null||d.windowIcon.isEmpty()?{}:{icon:d.windowIcon} null guard
• i==null||i.isEmpty()?null:i.resize( null guard
• windowIcon:i??null coalescing
• Idempotency (patch applied twice produces identical output)
• Output is valid JavaScript (new Function(patched) does not throw)

Limitations / follow-up

• The icon asset path (content/webview/assets/app-test.png) is resolved at patch time from context.iconPathExpression; if the upstream DMG renames the asset this patch will silently fall back. A follow-up could add a CI assertion that the asset path resolves.
• Patch is optional policy; if the minified signature drifts significantly only the null-safety guards (string-replace based) will still apply.

[ilysenko]

Reviewed locally and against the current upstream DMG patch report. CI is green and no blockers were found.