fix(brand): preserve application icon artwork across surfaces

[GCWing]

Summary

Preserve the application artwork independently from the startup logo so asset regeneration keeps the application, window, launcher, and browser icons consistent. The desktop tray now reuses the configured window icon on every desktop platform.

Type and Areas

Regression fix — brand asset generation, desktop/Tauri, installer, web UI, mobile web, relay, and native mobile resources.

Motivation / Impact

Keep the silver application mark as its own source, regenerate the PNG/ICO/ICNS outputs, and remove the separate macOS tray template. Startup and in-product logo assets retain their existing source.

Verification

• node --test scripts/generate-brand-assets.test.mjs — 10 tests passed.
• pnpm run fmt:rs --check — passed for the changed Rust file.
• cargo check -p openbitfun-desktop --lib — passed.
• git diff --check origin/1.0.0-explore...HEAD — passed.
• Rebased onto the latest target without conflicts; all 69 changed files retain the verified content.
• Browser automation, E2E, native visual checks, and platform packaging were not run.
• Remote workspace, remote control, Peer Device Mode, and Detached Dispatch were not exercised.

Reviewer Notes

AI-assisted; lightly tested with focused asset tests and a desktop compile check. Native tray appearance, including macOS light/dark menu bars, remains unverified.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• Asset documentation is updated; user-facing strings and locales are unchanged.