feat: native x-implemented-by routing

[belfzclaw]

Summary

• honor x-implemented-by directly in Router and transports
• add WebSocket client proxy/outbound support without plugins
• include bidirectional examples and tests

[codecov]

Codecov Report

❌ Patch coverage is 96.55172% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 97.92%. Comparing base (8531407) to head (dbc036e).

Files with missing lines	Patch %	Lines
src/router.ts	95.00%	2 Missing ⚠️
src/transports/websocket.ts	97.26%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #873      +/-   ##
==========================================
- Coverage   98.96%   97.92%   -1.04%     
==========================================
  Files           9        9              
  Lines         289      385      +96     
  Branches       43       66      +23     
==========================================
+ Hits          286      377      +91     
- Misses          3        8       +5     

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