Closes#172. Scenario files in bin/scenarios/ can now be authored as
.json instead of .bin — the server compiles them to wire format on
load, falling back to .bin if no .json is present.
- Add ParseScenarioBinary / CompileScenarioJSON in scenario_json.go;
supports sub-header format (strings as UTF-8, metadata as base64),
inline format, and raw JKR blobs.
- Add PackSimple JKR type-3 (LZ77) compressor in jpk_compress.go,
ported from ReFrontier JPKEncodeLz.cs; round-trip tested against
UnpackSimple.
- Fix off-by-one in processDecode (jpk.go): last literal byte was
silently dropped for data that does not end on a back-reference.
- Wire loadScenarioBinary into handleMsgSysGetFile replacing the
inline os.ReadFile call; mirrors the existing loadQuestBinary pattern.
- Rewrite docs/scenario-format.md with full container/sub-header spec
and JSON schema examples.
