Use the Clash C across brand surfaces

[hrhrng]

What changed

• replace the agent-face mark with the coral Clash C across the website, app chrome, install icons, and packaged desktop icon
• publish cache-busted favicon, Apple Touch Icon, and manifest assets
• correct the GitHub social preview while preserving Canvas, Timeline, and Director Stage
• add brand-contract regression coverage

Why

The product logo is the Clash wordmark: the C carries the theme color. Canvas, Timeline, Director Stage, and agent tooling remain product surfaces, not the identity mark.

Validation

• focused Vitest brand, landing, route, navigation, theme, and desktop packaging contracts
• Web production build
• Web ESLint and type-check
• Web UI and Desktop type-check
• final PNG and desktop icon visual inspection