Docs: README and repo hygiene (2026-09-25 audit)

[pietechsolution]

Held for review. Please do not merge yet.

Changes

• Tests: a real company name used as the demo brand is now the neutral "Riverside Hall" in picker-cart-lane.test.ts and picker-cart-lane-renderer.test.ts, and the asserted initial is updated from P to R.
• design/picker-spec.md: internal decision notes removed and each rule stated neutrally. "What it unlocks" -> "What it enables".
• src/ and test/: internal decision comments rewritten neutrally. Comments only, no behaviour change.
• README first paragraph now says what the SDK is (React Native seat map SDK for React Native and Expo), followed by a short company line. Every README em dash rewritten.

Checks

• pnpm check:public-hygiene passed (333 files), pnpm check:source-size passed, pnpm typecheck passed.
• pnpm test: 102 files, 978 tests passed.