Migrate the v3 Windows runtime from pkg/edge to the generated pkg/webview2 bindings

[taliesin-ai]

Goal

Migrate the Wails v3 Windows runtime from the hand-maintained pkg/edge bindings to the generated pkg/webview2 bindings, then retire pkg/edge.

Background

PR #5768 landed the overhauled binding generator and the generated bindings at v3/internal/webview2/pkg/webview2 (following the module fold #5711). Those bindings are currently dormant — nothing in the runtime imports them; the runtime still drives WebView2 entirely through pkg/edge + webviewloader.

The generated bindings are validated at their own layer (100%-covered generator, 1,020+ hermetic ABI tests, a live smoke test against the real DLL, and three example apps), but they have not been exercised as the production WebView2 driver.

Plan (from v3/internal/webview2/ARCHITECTURE.md)

1. Land the generator + tested pkg/webview2 — done in feat(webview2): port generator overhaul, generated tests and examples to v3/internal/webview2 #5768.
2. Refactor v3/pkg/application/... (chromium.go and friends) to import pkg/webview2 instead of pkg/edge.
3. Carry forward the pkg/edge runtime behaviour that the generator does not produce (it emits bindings, not orchestration/policy):
   • transient COM-error recovery (fix(webview2): recover from transient runtime COM errors instead of exiting #5658)
   • non-fatal SetSize/PutBounds (fix(webview2): never treat a failed SetSize/PutBounds as fatal #5597)
   • Focus() guard until controller init (fix(webview2): guard Focus() until controller initialisation completes #5568)
   • mixed-DPI monitor-scale detection ([v3][windows] Re-enable WebView2 monitor-scale detection to fix mixed-DPI GPU-process crash (#5732) #5734)
   • non-client-region / custom hit-test support (feat(windows): add support for custom hit-test logic for non-client regions #5462) and host-owned rasterization scale (fix(v3/windows): keep host-owned rasterization scale under visual hosting #5761)
   • the by-value-double ABI fix (fix(webview2): pass by-value COM doubles as bit patterns, not pointers #5741) is already correct-by-construction in the generated bindings.
4. Once the runtime is on pkg/webview2, move/remove pkg/edge.

Testing considerations

• Fix the flaky pkg/edge integration test TestCookieManager while migrating (it CoInitializes without runtime.LockOSThread(), so a goroutine thread-migration mid-test yields "CoInitialize has not been called" and hangs to the 10-minute timeout — observed on CI).
• Add real-DLL coverage across more than the handful of interfaces the live smoke test exercises today.