v0.4.15: split per-video vs total cache cap; auto-augment legacy config

- max_preload_mb is now strictly the per-video download cap (default raised
  to 2048 MB so a single 4K short clip fits without hitting the wall).
- New max_cache_mb knob caps total client-side cache directory size
  (default 750 MB, sized for ~50 short FHD clips). Enforced cooperatively
  at start of each /videoPreload download and during the read loop so a
  late-arriving large clip can't blow past the cap.
- VideoPlayerConfig.load() now detects missing keys (max_preload_mb,
  max_cache_mb, render_distance_blocks) and rewrites the file once with
  defaults filled in, so existing servers pick up new options without
  having to delete config/video_player.json.
- CachePolicyPayload now carries (maxPerVideoBytes, maxCacheBytes,
  renderDistanceBlocks); StreamCodec order: VAR_LONG, VAR_LONG, VAR_INT.
- Client receiver wires both caps into VideoCache; chat errors distinguish
  "단일 영상 NMB 초과" vs "전체 캐시 NMB 초과".
- Add dist/ to .gitignore (release artifacts uploaded to Gitea, never
  committed).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gradle.properties

@@ -5,7 +5,7 @@ org.gradle.configuration-cache=false
 
 # Mod
 mod_id=video_player
-mod_version=0.4.14
+mod_version=0.4.15
 maven_group=com.ejclaw.videoplayer
 archives_base_name=video_player