[docs] Add launch FAQ from first-user feedback

[Seven128]

Collect confusing points from the first launch posts and convert repeat questions into concise docs.

Acceptance signals:

• Adds only durable FAQ entries, not one-off support transcripts.
• Covers install/init, hidden dot-directory visibility, Context vs tests, when to update Context, and how to verify success.
• Uses language that is understandable to AI coding agent users who have not read PROJECT_SPEC.md.
• Keeps benchmark and award/star claims out unless supported by fresh evidence.
• Links [launch] Share adoption reports and missing recovery facts #4 for adoption reports and missing recovery facts.