feat(macos): refresh app icon and start page

[SarthakWade]

Summary

• generate a full-bleed cream H app icon over the normal wave palette and rebuild it when the renderer changes
• redesign normal and private start pages with responsive wave artwork, clear private-session messaging, and no external assets
• improve the address HUD with readable text, website-only dimming and blur, persistent homepage behavior, reliable outside-click dismissal, and race-safe transitions
• add native regression coverage for normal/private start pages and homepage/website HUD behavior

Validation

• pnpm test (67 protocol/security tests, secure prompt tests, MCP integration)
• pnpm test:runtime
• pnpm --filter @headless/web lint
• pnpm build
• zsh -n apps/headless/Tests/macos-e2e.sh
• swiftc -parse apps/headless/main.swift
• swiftc -parse apps/headless/tools/make-icon.swift
• pnpm test:e2e:mac passes the new start-page/HUD scenarios, menu actions, and WebKit conformance; the later existing durable-profile check locally restores its cookie but not its local-storage marker

[yashranaway]

Reviewed the full diff. Start page stays script-free under a strict CSP, no network, no committed rasters. Icon regen only fires when the renderer changes. E2E additions are test-only. Runtime suite green locally, full CI green. Merging.