Feature/dcw vae controls and fixes

[FrancoCotter]

Summary

This Pull Request introduces a comprehensive upgrade to the parameter mapping layers, frontend user interface, and backend CLI executors to align with the latest 78-dimensional parameters schema of the ACE-Step 1.5 core library, fully unlocking Dual Conditioning Wavelet (DCW) and VAE checkpoint customizability.

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Key Changes

1. Align API with Latest 78-Dimensional Gradio Payload

• Expanded Parameter Slots: Upgraded the Gradio arguments mapping in server/src/services/acestep.ts from 51 slots to 78 slots (Index 0 to 77).
• Enabled Advanced Parameters: Mapped newly exposed features including:
  • DCW controls (Enabled status, Wavelet Base, Mode, Scaler, and High Scaler)
  • Audio Formats: Custom timesteps, MP3 bitrates, and sample rates.
  • Stem Conditioning: Dynamic track_name and complete_track_classes.
  • Latent & Repaint Features: Normalization, Fades, Repaint modes, Retake seeds, and Flow Edit morphing properties.
• Type Coercion Alignment: Updated string/object boundary checks inside arguments mapping to prevent runtime serialization mismatch.

2. Enhanced Python CLI Fallback & Env Auto-Detection

• Config & Environment Loaders: Implemented .env environment loading inside server/scripts/simple_generate.py to respect system-level device and optimization overrides.
• 4B Parameter LLM Integration: Added native support, path mapping, and automatic download triggers for the newest acestep-5Hz-lm-4B model alongside the original 0.6B and 1.7B files.
• Command-line Controls: Added --vae-checkpoint, --dit-model, --no-dcw, and DCW scaling switches, allowing the CLI runner to perfectly match Gradio's state-driven logic.

3. Data Flow Bug Fixes

• Stems Conditioning Restored: Resolved a parameter omission where complete_track_classes was missing inside the UI generation dispatch (App.tsx) and backend API endpoint (server/src/routes/generate.ts), ensuring multitrack rendering functions exactly as intended.

4. UI/UX Refinement & Layout Upgrades (CreatePanel.tsx)

• Uncluttered VAE Selection: Moved the VAE selector out of the crowded model selection bar into its own separate, elegant row.
• Premium DCW Settings Panel: Replaced checkboxes with a sleek pill-toggle component that dynamically expands/collapses detailed configuration inputs (Wavelet Base dropdown, DCW Mode selection, and fine-grained Scaler sliders).

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Verification & Testing

• Checked standard compilation of types and front-end interface components.
• Verified parameter serialization formats against the latest Gradio layout structures.
• Tested CLI fallback executors for custom models (--dit-model) and custom VAEs (--vae-checkpoint).