feat: add ssr fallback flag info to response header

[lianxuify]

trafficstars

Summary

Touch SSR Fallback

forceCSR config + open with req params
?csr=1 
req header x-[framework like: pia]-ssr-fallback:1  

Hit SSR Fallback

res header x-[framework like: pia]-ssr-fallback: 1;reason=xxx
// reason:  query || header || error

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Checklist

• [ ] I have added changeset via pnpm run change.
• [ ] I have updated the documentation.
• [ ] I have added tests to cover my changes.

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⚠️ No Changeset found

Latest commit: 63e35082c4a1dd2c298397cedb402037a12e117e

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[zllkjc]

Thanks ! @GiveMe-A-Name cc.

And the branch has some conflicts now.

[lianxuify]

Thanks ! @GiveMe-A-Name cc.

And the branch has some conflicts now.

done