feat: add SenseNova U1.5 support (#1935)

docs/sensenova_u1.md

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+# How to Use
+
+SenseNova U1.5 is an 8B MoT model that performs diffusion directly in RGB pixel
+space. It does not require a separate text encoder or VAE.
+
+## Download weights
+
+- Download SenseNova U1.5 8B MoT
+    - safetensors: https://huggingface.co/sensenova/SenseNova-U1.5-8B-MoT
+
+Pass the complete downloaded repository directory to `--model`. The directory
+must contain `model.safetensors.index.json`, every referenced Safetensors shard,
+and the tokenizer files.
+
+## Examples
+
+### CUDA
+
+```bash
+./bin/sd-cli \
+  --model /path/to/SenseNova-U1.5-8B-MoT \
+  --prompt "a red cube on a white background" \
+  --width 2048 \
+  --height 2048 \
+  --steps 50 \
+  --cfg-scale 4 \
+  --flow-shift 3 \
+  --seed 42 \
+  --sampling-method euler \
+  --rng cuda \
+  --fa \
+  --output output.png
+```
+
+## Notes
+
+- To match the official non-thinking text-to-image pipeline, use 50 Euler
+  steps, CFG 4, flow shift 3, seed 42, CUDA RNG, and an empty negative prompt.
+- Width and height must be multiples of 32. The trained 1:1 resolution is
+  2048x2048; lower resolutions are useful for smoke tests but are outside the
+  training buckets.
+- The SenseNova prompt template and unconditional prompt are built
+  automatically.
+- This implementation supports non-thinking text-to-image generation. Image
+  editing, visual understanding, interleaved generation, and thinking-mode
+  prompt expansion are not implemented.