feat: support GGUF export for non-PEFT models + fix venv_t5 switching for local checkpoints (#4455)

* feat: support full model GGUF export, disable incompatible methods in UI

* fix: resolve base model from config.json for venv_t5 export switching

* feat: detect BNB-quantized models and disable all export methods for quantized non-PEFT checkpoints

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* [pre-commit.ci] auto fixes from pre-commit.com hooks

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* fix: relocate Ollama Modelfile alongside GGUFs during non-PEFT export cleanup

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

studio/backend/models/models.py

@@ -41,6 +41,10 @@ class ModelCheckpoints(BaseModel):
         None,
         description = "LoRA rank (r) if applicable",
     )
+    is_quantized: bool = Field(
+        False,
+        description = "Whether the model uses BNB quantization (e.g. bnb-4bit)",
+    )
 
 
 class CheckpointListResponse(BaseModel):