Upgrade dependencies and build pipeline

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

build: emit lib/ and UMD bundles via tsdown instead of tsc + Vite

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

build: single tsdown build; drop Vite lib config and rimraf

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

chore: upgrade to TypeScript 7 for native-speed noEmit typechecking

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs: update build commands for tsdown + TypeScript 7

Also pin useDefineForClassFields: false to preserve v11 class-field
semantics now that target is es2022.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Remove superpowers