fix(gaps): G0/G2/G5/G8 — eliminate unimplemented! panics, re-enable rtx-distributed, rtx-tts, fix multimodal forward

G0 (Critical): Replace 45 unimplemented!() panics across three GPU backends
- rtx-backend-cuda: sin/cos/tanh via PTX, relu/sigmoid/leaky_relu/elu via activation.rs,
  pow/clamp/gt_scalar via unary.rs, var/var_dim host-side, conv2d/max_pool2d/avg_pool2d
  CPU fallback in new ops/conv.rs; new PTX kernels in element_wise.cu
- rtx-backend-rocm: all 15 ops via CPU round-trip (to_vec → compute → from_slice)
- rtx-backend-sycl: all 15 ops via CPU round-trip (to_host → compute → from_data)

G2 (High): Re-add rtx-distributed to workspace
- Vendor 4 minimal RNCCL stub crates at crates/vendor/rnccl/*
- Update rtx-distributed RNCCL path deps to point at stubs (../../../../RNCCL/* → ../../vendor/rnccl/*)
- Remove rtx-distributed from workspace exclude list, add to members

G5 (Medium): Re-enable rtx-tts (213 tests restored)
- Fix 15 rtx-nn API drift issues: LayerNorm::new, Conv1d::from_config, Conv1dPadding::Zeros,
  Dropout::new(p, device), tensor methods (relu/tanh/sigmoid/cat/stack), squeeze(Some(n)),
  to_vec() turbofish removal, Tensor::randn with &[...] slices

G8 (Low): Quantum stubs + multimodal forward bug
- rtx-timeseries: remove dead quantum/neuromorphic TODO comment blocks (no module files exist)
- rtx-multimodal/fusion/transformer.rs: wire TransformerBlock loop in forward()
- rtx-multimodal/fusion/strategies.rs: wire bottleneck_layers loop in forward()
- rtx-transformers/architectures/transformer_block.rs: add forward() method (pre-norm residuals;
  full attention+FFN pending when those sub-layers are wired)

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

crates/vendor/rnccl/rnccl-transport/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "rnccl-transport"
+version = "0.1.0"
+edition = "2024"
+description = "Stub — real RNCCL at github.com/rustyverse/rnccl"
+license = "MIT OR Apache-2.0"