Add automatic request-ID propagation for Suspense

[arthurfiorette]

Summary

• add AutoSuspense for boundaries that obtain their request ID from an automatic Suspense scope
• add the opt-in autoSuspense option to the Express and Fastify integrations
• preserve the existing Suspense API with its required explicit rid
• isolate concurrent request scopes across awaited route handlers
• document automatic and explicit Suspense usage
• raise the @kitajs/html Node.js minimum to 12.17 for AsyncLocalStorage

Implementation

Framework integrations establish the automatic scope before route JSX is evaluated. AutoSuspense reads the request ID from that scope and throws with setup guidance when no scope is active. Regular Suspense remains unchanged for users who prefer explicit request IDs.

Testing

• pnpm format
• pnpm build
• pnpm test-types
• pnpm test
• pnpm -F @kitajs/docs-html build

Includes core, Express, and Fastify coverage for missing scopes, missing request IDs, type safety, awaited handlers, and concurrent request isolation.

[changeset-bot]

🦋 Changeset detected

Latest commit: d95c304

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

This PR includes changesets to release 3 packages

Name	Type
@kitajs/html	Minor
@kitajs/fastify-html-plugin	Minor
@kitajs/express-html-plugin	Minor

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.54%. Comparing base (b46042c) to head (d95c304).

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #515      +/-   ##
==========================================
+ Coverage   95.40%   95.54%   +0.13%     
==========================================
  Files          13       13              
  Lines         479      494      +15     
  Branches      137      141       +4     
==========================================
+ Hits          457      472      +15     
  Misses         20       20              
  Partials        2        2              

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