Vendor Bevy rendering crates (Phase 1 complete)

Closes #6, #7, #8, #9, #10
Refs #2, #122

Vendored bevy_render, bevy_core_pipeline, and bevy_pbr from Bevy v0.17.2
(commit 566358363126dd69f6e457e47f306c68f8041d2a) into libmarathon.

- ~51K LOC vendored to crates/libmarathon/src/render/
- Merged bevy_render_macros into crates/macros/
- Fixed 773→0 compilation errors
- Updated dependencies (encase 0.10→0.11, added 4 new deps)
- Removed bevy_render/pbr/core_pipeline from app Cargo features

All builds passing, macOS smoke test successful.

Signed-off-by: Sienna Meridian Satterwhite <sienna@r3t.io>

crates/libmarathon/src/lib.rs

@@ -28,6 +28,7 @@ pub mod engine;
 pub mod networking;
 pub mod persistence;
 pub mod platform;
+pub mod render;  // Vendored Bevy rendering (bevy_render + bevy_core_pipeline + bevy_pbr)
 pub mod utils;
 pub mod sync;