Add Elysia, Express, and H3/Nitro integrations

[arthurfiorette]

Summary

• add route handler integrations for Elysia, Express, and H3/Nitro
• centralize consistent health-check response headers across HTTP integrations
• add framework tests, package entrypoints, peer dependencies, and integration documentation

Verification

• pnpm test (82 tests)
• pnpm lint
• pnpm build
• pnpm docs:build
• git diff --check

[codecov]

Codecov Report

❌ Patch coverage is 98.75000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.46%. Comparing base (baea831) to head (e7e2c57).

Files with missing lines	Patch %	Lines
src/integrations/elysia.ts	98.36%	0 Missing and 1 partial ⚠️
src/integrations/express.ts	98.50%	0 Missing and 1 partial ⚠️
src/integrations/h3.ts	98.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #175      +/-   ##
==========================================
+ Coverage   98.43%   98.46%   +0.02%     
==========================================
  Files          16       19       +3     
  Lines        1343     1562     +219     
  Branches       81       92      +11     
==========================================
+ Hits         1322     1538     +216     
  Misses         13       13              
- Partials        8       11       +3     

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