* feat(studio): offer MLX-supported optimizers on Apple Silicon
The training form's optimizer dropdown only listed CUDA/bitsandbytes optimizers (adamw_8bit, paged variants, torch fused). On Apple Silicon the MLX trainer supports a different set (adamw, adam, lion, muon, sgd, adafactor) and remaps every bitsandbytes/torch name to plain AdamW, so the dropdown misrepresented what actually runs.
Offer the MLX optimizer list when the device is a Mac, and derive the displayed value so the control is never blank: the shared CUDA default and the other bitsandbytes/torch options render as AdamW (exactly how the MLX backend normalizes them), while any other value is shown as-is so an unrecognized or non-canonical imported optimizer is never mislabeled. Non-Mac behavior is unchanged. The run-summary optimizer label now resolves from both lists.
* feat(studio): show an MLX-appropriate optimizer tooltip on Apple Silicon
The optimizer tooltip described "8-bit variants" and recommended "Fused" for vision models, neither of which is offered when training runs on MLX. On Apple Silicon, show a tooltip that matches the MLX optimizer set and notes that Lion typically needs a lower learning rate than AdamW.
Copy-only: no change to the selected optimizer or the learning rate, and the non-Mac tooltip is unchanged. The new string is added to the English locale; other locales fall back to English until translated, matching how new keys are handled elsewhere.
* fix(studio): label Mac CUDA-alias optimizers as AdamW in the run summary
On Apple Silicon the run-configuration summary looked up the stored optimizer name directly, so a run that kept a CUDA/bitsandbytes default such as adamw_8bit was labeled "AdamW 8-bit" even though the picker shows "AdamW" and the MLX backend runs plain AdamW. Mirror the training form's derivation so those aliases are labeled AdamW in the summary too.
Display-only: no change to the stored or submitted optimizer, and non-Mac summaries are unchanged.
* feat(studio): disable LoftQ and sequence packing on Apple Silicon
Neither LoftQ nor sequence packing is supported on MLX — the backend rejects LoftQ and the trainer silently forces packing off — yet the training form still offered both on Apple Silicon.
Disable the LoftQ LoRA-init option (greyed and unclickable, with an inline "Not supported on Apple Silicon" note) and the "Enable packing" checkbox (greyed, with a tooltip explaining why), matching how the unsupported "Enable streaming" control is presented. Clearing effects reset a stale loftq/packing value to its default on Mac so the disabled controls never submit it. Non-Mac behavior is unchanged.
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