fix(fallbacks): clarify API docs and release workflow

[caio-pizzol]

Clarifies the public docs around the 0.2 fallback API and removes stale wording from the package README.

Why:

• the docs should lead with the three supported use cases: render a family, explain a decision, and create a resolver map
• public wording should describe supported runtime files instead of internal measurement details
• release should run automatically when releasable commits land on main, while keeping manual dry-run support

Verified:

• bun run check
• stale API scan for getFallback, deriveFallbackMap, hasFamily, and faithful