build: replace tsup with tsdown and apply React Compiler to published dist

[acasazza]

Why

• tsup is in maintenance mode; tsdown (rolldown-based) is its designated successor.
• Faster builds.
• The old tsup config had a babelOptions key that tsup silently ignored — babel-plugin-react-compiler was never actually applied to any published artifact. This PR makes it real: 9 compiled functions in hooks, 134 in react-components (target: '19').

What changed

• All three packages (core, hooks, react-components) build with tsdown ^0.22.4; the compiler is wired via @rolldown/plugin-babel + reactCompilerPreset() (official tsdown recipe).
• Regression guard: build runs a check-compiler assertion that react/compiler-runtime is present in both dist files, so a silently-skipped compiler can never ship again. All three packages now have uniform ci scripts; react-components gains the attw --pack exports check it was missing.
• Output parity with tsup: identical filenames (fixedExtension: false), identical exports maps, "use client" banner, and an externals diff of exactly one line — react/compiler-runtime. platform: 'browser' on react-components keeps rolldown's require-interop shim browser-safe (the node default emits a top-level node:module import that breaks consumer bundles).
• hooks peer range tightened to react >=19.0.0 (compiled output imports the built-in compiler runtime) — ⚠️ breaking, flag as major at the next make:version.
• prop-types removed from react-components: its untyped import broke the rolldown dts build, and all its validators were dead code (the published dist had zero trace of them). One internal type rewritten as a plain interface; public types unchanged.

Verification

• Unit tests: 766 + 145 + 129 pass; attw green on all resolution modes for all three packages; pnpm typecheck reports the same pre-existing error set as before (no additions).
• E2E: mfe-checkout (linked dist, React 19.2.7) ran guest-addresses.spec.ts 12×/12 clean — better than the 11/12 tsup baseline.

Note: mfe-checkout needed a React 18.3.1 → 19.2.7 upgrade to consume the compiled dist (React 18 has no react/compiler-runtime); that change lives in the mfe-checkout repo and is not yet committed there.

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