(signals-react): Remove automatic entrypoint

[JoviDeCroock]

Resolves #637

This is a major change, we are removing the automatic entry-point due to React 19 incompatibilities. We have considered this entry-point deprecated ever since moving to the Babel integration.

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[github-actions]

Size Change: -243 B (-0.29%)

Total Size: 83.1 kB

Filename	Size	Change
docs/dist/assets/client.********.js	46.1 kB	-243 B (-0.52%)

ℹ️ View Unchanged

Filename	Size
docs/dist/assets/bench.********.js	1.59 kB
docs/dist/assets/index.********.js	836 B
docs/dist/assets/jsxRuntime.module.********.js	284 B
docs/dist/assets/preact.module.********.js	4.03 kB
docs/dist/assets/signals-core.module.********.js	1.41 kB
docs/dist/assets/signals.module.********.js	2.16 kB
docs/dist/assets/style.********.js	21 B
docs/dist/assets/style.********.css	1.24 kB
docs/dist/basic-********.js	243 B
docs/dist/demos-********.js	3.44 kB
docs/dist/nesting-********.js	1.13 kB
docs/dist/react-********.js	242 B
packages/core/dist/signals-core.js	1.45 kB
packages/core/dist/signals-core.mjs	1.47 kB
packages/preact/dist/signals.js	1.46 kB
packages/preact/dist/signals.mjs	1.43 kB
packages/react-transform/dist/signals-*********.js	4.93 kB
packages/react-transform/dist/signals-transform.mjs	4.16 kB
packages/react-transform/dist/signals-transform.umd.js	5.04 kB
packages/react/dist/signals.js	188 B
packages/react/dist/signals.mjs	150 B

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