The installed app's description says what the front page says #6045

Intent: one sentence for what the forge is, wherever it is read.

Seen: /manifest.webmanifest says "Your code, your machine."; the front page says "Apps, live. A software forge that builds and serves its own apps."

Done:

• [ ] the manifest's description, the front page's meta description and og:description come from one constant
• [ ] a test asserts the manifest and the front page carry the same sentence

Files: src/web/standards.ts (manifest), the front page, one test. Risk: pick the front page's words; do not write new copy.