[Flight] Fix the react-server-dom-rspack package contract

[BleedingDev]

Summary

This PR is intentionally stacked within BleedingDev/react on SyMind#1. It should be reviewed after that PR and can be retargeted to SyMind/react:react-server-dom-rspack once it lands.

It addresses only the assembled react-server-dom-rspack package contract.

The package advertises ./plugin, but its wrapper requires a CJS artifact that the package does not build. Rspack’s compiler integration instead lives in @rspack/core through experiments.rsc.createPlugins().

This PR:

• removes the unresolved ./plugin export and wrapper;
• removes stale node-register, unbundled, and ESM template residue;
• restores loadServerAction on the browser server entrypoint;
• narrows Rspack host configuration to Rspack-owned modules;
• keeps the supported client, server, and static runtime entries;
• verifies package-root and non-react-server environment guards;
• verifies removed subpaths are private and unsupported files are absent from the npm inventory; and
• verifies conditional-export targets for workerd, deno, worker, node, edge-light, browser, and default conditions.

No working Rspack compiler or runtime implementation is removed. If maintainers prefer an intentionally implemented compatibility plugin entry, that decision can be handled here without blocking SyMind#1.

How did you test this change?

After an exact experimental release rebuild:

• Assembled-package suite, development: 8/8 passed.
• Assembled-package suite, production: 8/8 passed.
• Frozen-lockfile install passed.
• Targeted lint passed.
• Prettier check-changed passed.
• git diff --check passed.

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Changed Files

File	Status
packages/react-server-dom-rspack/package.json	34% smaller
package.json	0% smaller
packages/react-server-dom-rspack/npm/client.node.unbundled.js	0% smaller
packages/react-server-dom-rspack/npm/esm/package.json	0% smaller
packages/react-server-dom-rspack/npm/plugin.js	0% smaller
packages/react-server-dom-rspack/npm/server.node.unbundled.js	0% smaller
packages/react-server-dom-rspack/npm/static.node.unbundled.js	0% smaller
packages/react-server-dom-rspack/src/__tests__/ReactFlightDOMRspackPackage-test.js	0% smaller
packages/react-server-dom-rspack/src/server/react-flight-dom-server.browser.js	0% smaller
scripts/shared/inlinedHostConfigs.js	0% smaller