Import art/VFX asset packs + game-feel systems; normalize texture extensions to lowercase for LFS

Add BefourStudios SciFi environment packs, Gabriel Aguiar VFX, and the
ShaderCrew Toon Shader embedded packages, plus combat/enemy/wave/death
gameplay systems and supporting vault docs/screenshots.

Rename 11 vendor textures from uppercase .PNG/.HDR to lowercase so the
case-sensitive Git LFS filters (*.png/*.hdr) match on case-sensitive
filesystems (Linux CI, case-sensitive macOS), not just locally where
core.ignorecase=true masks the gap. Each .meta moved with its asset so
GUID references are preserved. All ~1000 binaries tracked via LFS.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Packages/manifest.json

@@ -18,6 +18,7 @@
     "com.unity.probuilder": "6.0.9",
     "com.unity.render-pipelines.universal": "17.4.0",
     "com.unity.services.multiplayer": "2.1.3",
+    "com.unity.shadergraph": "17.4.0",
     "com.unity.test-framework": "1.6.0",
     "com.unity.timeline": "1.8.12",
     "com.unity.ugui": "2.0.0",