- Move docs/porting-from-orjson.rst to docs/porting/orjson.rst
- Add docs/porting/index.rst as a landing page for future guides
- Add "Porting" toctree section in docs/index.rst
- Fix cross-references for the new file location
- Fix incorrect workarounds in "Features with no direct equivalent":
  OPT_OMIT_MICROSECONDS, OPT_PASSTHROUGH_DATACLASS,
  OPT_PASSTHROUGH_SUBCLASS
- Clarify pretty-printing two-step process

Both orjson and msgspec encode naive datetimes identically by default
(without timezone). OPT_NAIVE_UTC is an opt-in flag, not the default.