refactor(server-core): report CSR fallbacks through monitors

[GiveMe-A-Name]

Summary

• Remove the server plugin fallback hook, its compatibility runner, and related type exports.
• Report SSR-to-CSR fallback events directly through request monitors.
• Preserve existing fallback response headers and HTML reason injection.

Breaking change

Consumers must remove api.fallback(...). Fallback reporting is available through the request monitor warning and ssr-fallback counter events.

Verification

• pnpm --filter @modern-js/server-core test -- tests/plugins/render.test.ts
• pnpm --filter @modern-js/server-core build

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[changeset-bot]

🦋 Changeset detected

Latest commit: 796f5b6

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 119 packages

Name	Type
@modern-js/server-core	Patch
@modern-js/plugin-bff	Patch
@modern-js/plugin-data-loader	Patch
@modern-js/plugin-i18n	Patch
@modern-js/render	Patch
@modern-js/plugin-polyfill	Patch
@modern-js/prod-server	Patch
@modern-js/server-runtime	Patch
@modern-js/server	Patch
@modern-js/server-utils	Patch
@modern-js/app-tools	Patch
server-config	Patch
bff-api-app	Patch
bff-client-app	Patch
bff-indep-client-app	Patch
bff-hono	Patch
deploy-server	Patch
pure-esm-project	Patch
basic-app-rstest	Patch
i18n-app-csr-html-lang	Patch
i18n-app	Patch
i18n-app-ssr-html-lang	Patch
i18n-app-ssr	Patch
i18n-custom-i18n-wrapper	Patch
i18n-mf-app-provider	Patch
i18n-mf-component-provider	Patch
i18n-mf-consumer	Patch
i18n-routes	Patch
i18n-routes-ssr	Patch
@modern-js/plugin-ssg	Patch
server-esm-tsx	Patch
server-monitors	Patch
ssg-fixtures-web-server	Patch
ssr-base-test	Patch
ssr-base-fallback-test	Patch
ssr-useid-test	Patch
@modern-js/adapter-rstest	Patch
@modern-js/plugin-styled-components	Patch
@modern-js/image	Patch
@modern-js/runtime	Patch
@integration-test/alias-set	Patch
app-document	Patch
async-entry-test	Patch
tmp	Patch
integration-clean-dist-path	Patch
integration-compatibility	Patch
integration-custom-dist-path	Patch
custom-file-system-entry	Patch
integration-custom-template	Patch
deploy	Patch
dev-server	Patch
integration-disable-html	Patch
entries-app-builder	Patch
app-custom-entries	Patch
app-custom-routes-runtime	Patch
app-custom	Patch
app-entry	Patch
app-route	Patch
app-entry-server	Patch
@integration-test/image-component	Patch
main-entry-name	Patch
nonce	Patch
react-compiler-test	Patch
routes-match	Patch
routes	Patch
app-rsbuild-hooks	Patch
rsc-csr-app	Patch
rsc-csr-routes	Patch
rsc-ssr-app	Patch
rsc-ssr-routes	Patch
basic-app-rstest-browser	Patch
runtime-custom-plugin	Patch
runtime-custom-config-plugin	Patch
select-mul-entry-test	Patch
select-one-entry-test	Patch
server-json-script	Patch
server-prod	Patch
server-routes	Patch
@source-code-build/app	Patch
ssg-fixtures-mega-list-routes	Patch
ssg-fixtures-nested-routes	Patch
ssg-fixtures-simple	Patch
ssr-base-async-entry-test	Patch
ssr-base-async-pre-entry-test	Patch
ssr-base-json-test	Patch
init	Patch
ssr-base-loadable	Patch
ssr-partial-test	Patch
rsc-closing-tags-test	Patch
ssr-script-loading	Patch
ssr-streaming-inline-test	Patch
ssr-streaming-lazy-test	Patch
ssr-streaming-test	Patch
styled-components-stream	Patch
styled-components-string	Patch
integration-tailwindcss-v2	Patch
integration-tailwindcss-v3	Patch
integration-tailwindcss-v4-tools	Patch
integration-tailwindcss-v4	Patch
tmp-dir	Patch
write-to-dist	Patch
@modern-js/bundle-diff-benchmark	Patch
@modern-js/main-doc	Patch
@modern-js/tsconfig	Patch
@modern-js/builder	Patch
@modern-js/bff-core	Patch
@modern-js/bff-runtime	Patch
@modern-js/create-request	Patch
@modern-js/create	Patch
@modern-js/i18n-utils	Patch
@modern-js/plugin	Patch
@modern-js/runtime-utils	Patch
@modern-js/sandpack-react	Patch
@modern-js/types	Patch
@modern-js/utils	Patch
@modern-js/rslib	Patch
@scripts/prebundle	Patch
@scripts/rstest-config	Patch
@scripts/release-node	Patch

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