[codex] Preserve and document Land CMA PWA

[fik14]

What changed

• add preservation-focused documentation, usage guidance, and a valuation limitation notice
• repair manifest and Apple touch-icon paths
• use a repository-specific service-worker cache and precache icons
• fix the malformed KPI border-radius declaration
• escape values restored from imported JSON before placing them in HTML attributes

Why

The manifest referenced a missing icons/ directory, and imported values could break generated markup or inject HTML. These changes preserve the original app while making installation and file restoration safer.

Impact

The app remains dependency-free and its calculations, exports, and public URL are unchanged.

Validation

• git diff --check
• manifest parsed with python3 -m json.tool
• local HTTP smoke checks returned 200 for the app, manifest, and corrected icon assets