fix(app): register export logs globally

[opencode-agent]

Summary

• move logs.export into a dedicated desktop command registration mounted under the shared app CommandProvider
• keep desktop menu entries as normal command-backed items instead of duplicating Export Logs handling in each layout
• add a regression test that Export Logs remains wired through the desktop command registry

Tests

• bun test --preload ./happydom.ts ./src/desktop-menu.test.ts (from packages/app)
• bun typecheck (from packages/app)
• git push pre-push hook: bun turbo typecheck

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