feat(editor): add WMVC (Movie Credits Roll) — 112th open format

Novel replacement for the embedded credit-roll text
vanilla WoW carried inside the cinematic-renderer blob
(the post-cinematic credits that scroll up the screen
after each expansion intro). Each entry binds one
credits category (Production / Music / Voice Acting /
etc.) for one cinematic to its ordered list of credit
lines.

First catalog with a variable-length STRING array
payload — previous variable-length formats used int
arrays (WCMR waypoints / WCMG mutex spells / WPTT
rank-spells / WBAB rank chains / WRPR unlocked items +
recipes). The lines[] field serializes as count +
(length + bytes)* per line, mirroring how strings work
elsewhere in the catalog set just lifted into a per-
entry array.

Seven category enum values cover the full credit
taxonomy: Production / Music / Audio / Engineering /
Art / Voice / Special. Three preset emitters:
makeWotLKIntro (5 blocks for the WotLK Arthas/Terenas
cinematic with the actual canonical music credits —
Brower/Duke/Stafford/Hayes), makeQuestCinema (3-block
template for per-quest cinematics), makeStarterRoll
(4-block generic template).

orderHint sorts blocks within a single cinematic so
the renderer can render Production -> Direction ->
Music -> Voice -> Special Thanks in canonical order
without depending on entry order in the binary.

Validator's most novel checks combine string + grouping
constraints unique to credit rolls: per-cinematic
orderHint slot uniqueness — two blocks at the same
(cinematicId, orderHint) would render in non-
deterministic order due to the std::sort being stable
but content-order undefined. Per-line: empty lines
warn (would render as blank, intentional spacers
should use a placeholder character), lines >80 chars
warn (text-buffer wrap at the canonical 80-char
credit-renderer width).

Format count 111 -> 112. CLI flag count 1206 -> 1211.

tools/editor/cli_arg_required.cpp

@@ -344,6 +344,8 @@ const char* const kArgRequired[] = {
     "--gen-pcr", "--gen-pcr-stable", "--gen-pcr-warlock",
     "--info-wpcr", "--validate-wpcr",
     "--export-wpcr-json", "--import-wpcr-json",
+    "--gen-mvc", "--gen-mvc-quest", "--gen-mvc-starter",
+    "--info-wmvc", "--validate-wmvc",
     "--gen-weather-temperate", "--gen-weather-arctic",
     "--gen-weather-desert", "--gen-weather-stormy",
     "--gen-zone-atmosphere",