doc-tests harness: pass --app-bundle-id (and other widget-cross-compile flags) so home-screen widget targets become exercisable #194

Context

Surfaced during the v0.5.299 docs audit. The 8 home-screen-widget docs pages (docs/src/widgets/{overview,creating-widgets,components,configuration,data-fetching,platforms,watchos,wearos}.md) document a Widget({...}) API that is wired in HIR/codegen (crates/perry-hir/src/lower.rs::try_lower_widget_decl, plus perry-codegen-glance, perry-codegen-wear-tiles, perry-codegen-swiftui for the per-platform output).

The CLI accepts:

• --target ios-widget
• --target ios-widget-simulator
• --target android-widget
• --target watchos-widget
• --target watchos-widget-simulator
• --target wearos-tile

But the doc-tests harness can't drive these targets because:

1. Each requires --app-bundle-id and the harness's cross_compile_one (crates/perry-doc-tests/src/main.rs:621) doesn't surface that flag.
2. The host-LLVM target lowers Widget({...}) to a no-op at execution time, so a host run wouldn't certify any widget output even if the harness ran it.

Because of this, all 46 ,no-test fences across the 8 widget pages are kept un-verified — even though the codegen path is real and works when invoked manually with the right CLI flags.

What to do

Two pieces:

1. Banner-driven bundle-id config. Extend the per-example banner format (currently // platforms:, // targets:, // run: false) with a new directive:

// widget-bundle-id: com.example.perry-widget-demo

When the harness sees --target ios-widget (etc.) in the example's targets: list AND has a widget-bundle-id, invoke perry compile with --app-bundle-id filled in.

2. Cross-compile artifact check. Widget-target outputs are bundles or asset directories (.app / .apk / Tile.swift). Extend cross_compile_one's artifact-existence check to handle those layouts.

Acceptance criteria

• An example with // targets: ios-widget, android-widget, wearos-tile + a widget-bundle-id banner cross-compiles cleanly under the doc-tests harness on a host with the right SDKs (Xcode for iOS/watchOS, Android NDK for android-widget/wearos-tile).
• All 46 ,no-test fences across the 8 widget pages convert to verified {{#include}} extracts.
• The widget pages drop their "Status: API wired but harness can't drive it" callouts.
• CI matrix (.github/workflows/test.yml) gains a widget-targets job that runs the harness with the new flag plumbing on a macOS runner with Xcode installed.

Pointers

• Cross-compile entrypoint: crates/perry-doc-tests/src/main.rs:621 (cross_compile_one)
• Banner parser: crates/perry-doc-tests/src/main.rs:390+ (read_banner)
• Per-target validator: crates/perry-doc-tests/src/main.rs:574+ (target_buildable_reason)
• HIR widget lowering: crates/perry-hir/src/lower.rs::try_lower_widget_decl
• Widget codegen crates: crates/perry-codegen-glance, crates/perry-codegen-wear-tiles, crates/perry-codegen-swiftui
• Existing example with cross-compile targets banner: docs/examples/ui/styling/shadow.ts (uses // targets: ios-simulator, web, wasm).

Estimated size

Small — ~30-50 lines of harness code plus the matching CI step. The actual widget codegen is already done; this is purely test plumbing.