feat(kernel): add portable server networking support

[MikiEEE]

Summary

• classify non-blocking socket retries by operation and TLS direction while preserving bytes-like buffers for zero-copy sends
• add portable passive TCP server contracts, opaque addresses, Unix and conservative MicroPython implementations, and migrate the web demo
• add a coalescing scheduler wakeup channel with bounded EINTR handling, Unix socketpair support, and explicit unsupported behavior on generic MicroPython

Validation

• originating PRs: fix(kernel): classify socket retries by operation #38, feat(kernel): add passive TCP server abstractions #40, and feat(kernel): add scheduler wakeup channel #39
• static typing passed
• CPython 3.10-3.13 test matrix passed
• branch coverage passed
• built-distribution verification passed
• independent adversarial and critic reviews completed; actionable findings were resolved

Compatibility and residual risk

• required base-kernel TCP primitives now fail explicitly with NotImplementedError instead of returning plausible no-op values
• generic MicroPython wakeup channels remain explicitly unsupported pending a portable interrupt-safe primitive
• on-device MicroPython validation remains outstanding