resourcepack: declare compatibility range from 1.21.6 to latest known

Pack.mcmeta now spans pack_format MIN_SUPPORTED_FORMAT (=63, 1.21.6) up to
max(LATEST_KNOWN_FORMAT, resolved.format) so a single build loads on every
MC from 1.21.6 through 26.1.2+ (currently extending to 86 = 26.2). Both
schemas are written: supported_formats for clients on pack_format <= 64,
and min_format/max_format for 1.21.9+ clients. pack_format itself stays
at the build target so newer clients see the pack as current rather than
legacy.

src/installer-rp/packFormat.ts

@@ -24,6 +24,12 @@ const TABLE: Array<readonly [string, number]> = [
 /** 테이블에서 마지막(=최신) 항목의 포맷. 알 수 없는 mcVersion 에 대한 폴백. */
 export const LATEST_KNOWN_FORMAT: number = TABLE[TABLE.length - 1][1]
 
+/**
+ * 리소스팩이 호환된다고 선언할 최소 pack_format.
+ * 1.21.6 (=63) 부터를 지원 범위 하한으로 둔다.
+ */
+export const MIN_SUPPORTED_FORMAT = 63
+
 export interface ResolvedFormat {
   /** 매칭된 mcVersion 키 (없으면 null). */
   matched: string | null