Expand project favicon resolution to support PWA manifests and directory scanning

[Brechard]

Summary

The current ProjectFaviconResolver already handles well-known favicon paths and explicit t3.json / <link rel="icon"> declarations, but it misses two common icon sources:

1. PWA manifest.json / site.webmanifest files that declare icons arrays.
2. Projects that place icon files in asset directories without explicitly referencing them in source files (e.g. images/icon.png, assets/logo.svg, static/favicon.ico).

Proposed change

• Parse manifest.json, public/manifest.json, site.webmanifest and public/site.webmanifest for icon src entries, preferring the largest declared icon size.
• Add a directory-scan fallback over common asset folders (public, app, src, src/app, assets, static, resources, images, img, media, app-icon, .idea) looking for well-known icon filenames with a priority by name and extension.
• Extend the ProjectFaviconResolutionError operations to cover read-manifest and scan-directory.
• Add unit tests for both new detection paths.

This improves icon coverage for PWAs, monorepos and projects that keep icons under arbitrary asset folders.