Add SJISToUTF8Lossy() that wraps SJISToUTF8() and logs decode errors at
slog.Debug level. Replace all 31 call sites across 17 files that previously
discarded the error with `_, _ =`. This makes garbled text from malformed
SJIS client data debuggable without adding noise at default log levels.
Add package-level documentation (doc.go) to all 22 first-party
packages and godoc comments to ~150 previously undocumented
exported symbols across common/, network/, and server/.
UTF8ToSJIS panicked when encountering characters outside the Shift-JIS
range (emoji, Lenny faces, cuneiform, etc.), crashing the server when
such characters were sent via the Discord relay channel.
Replace the panic with graceful filtering that drops unmappable runes
and preserves valid content. Also fix ToNGWord index-out-of-range panic
on empty encoder output.
Closes#116
