fix(jepa-vision-bridge): add as_any/as_any_mut to RtxVisionJepaEncoder

Required by JepaEncoder trait update in batch29 (as_any for downcasting).

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

crates/training/rtx-transformers/src/ssl/jepa_vision_bridge.rs

@@ -52,6 +52,9 @@ impl RtxVisionJepaEncoder {
 
 #[cfg(feature = "vision-bridge")]
 impl JepaEncoder for RtxVisionJepaEncoder {
+    fn as_any(&self) -> &dyn std::any::Any { self }
+    fn as_any_mut(&mut self) -> &mut dyn std::any::Any { self }
+
     fn encode(&self, patch_indices: &[usize]) -> Vec<f32> {
         // Returns zeros with correct shape [n_patches, embed_dim].
         // Real values come when ViT::encode_patch_indices uses GPU tensor ops.