Phase B of #188. Quest JSON title/description/text_main/text_sub_a/
text_sub_b/success_cond/fail_cond/contractor now accept either a plain
string (existing behaviour) or a language-keyed object like
"title": { "jp": "...", "en": "...", "fr": "..." }
CompileQuestJSON takes the compiling session's language and resolves
each field through a fallback chain (requested -> plain -> jp -> en ->
any non-empty), so existing single-language quest JSONs keep working
byte-for-byte unchanged.
The quest cache is re-keyed on (questID, language) so compiled binaries
for different languages never leak between sessions on a multi-language
server. loadQuestBinary and loadQuestFile now pass s.Lang() into both
the compiler and the cache.
ParseQuestBinary emits plain-string LocalizedStrings, so the
binary -> JSON -> binary round-trip still produces identical output.
The new LocalizedString type lives in its own file and is reusable by
phase C (scenarios, mail templates, shop text). Shift-JIS encoding
still applies to the wire format, so localized values must use
characters representable in Shift-JIS — ASCII, kana, CJK — which is
documented on the type.
Adds human-readable JSON as an alternative quest format for bin/quests/.
The server tries .bin first (full backward compatibility), then falls back
to .json and compiles it to the MHF binary wire format on the fly.
JSON quests cover all documented fields: text (UTF-8 → Shift-JIS),
objectives (all 12 types), monster spawns, reward tables, supply box,
stages, rank requirements, variant flags, and forced equipment.
Also adds ParseQuestBinary for the reverse direction, enabling tools to
round-trip quests and verify that JSON-compiled output is bit-for-bit
identical to a hand-authored .bin for the same quest data.
49 tests: compiler, parser, 13 round-trip scenarios, and golden byte-
level assertions covering every section of the binary layout.
