Add release notes for v0.92 and refactor mixed filament gradient handling

- Introduced a new `RELEASE_NOTES_v0.92.md` file detailing highlights such as gradual gradient behavior, mixed filament indexing fixes, and editable automatic mixed filaments.
- Refactored `compute_gradient_ratios` to remove the cycle layers parameter, implementing a new gradual integer cadence for gradient transitions.
- Updated `MixedFilament` structure to include an `origin_auto` flag for better management of auto-generated entries.
- Adjusted related parsing, serialization, and UI handling to reflect these changes, ensuring improved user experience and color fidelity in mixed filament rendering.

RELEASE_NOTES_v0.92.md

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+# Snapmaker Orca Full Spectrum v0.92 (Pre-release)
+
+Mixed-filament stability and workflow release.
+Based on Snapmaker Orca v2.2.4.
+
+## Highlights
+
+### Gradient Behavior Is Now Gradual
+- Removed the `Mixed filament layer cycle` setting.
+- Reworked non-height-weighted gradient math to use gradual integer cadence by ratio (minority side anchors to 1 layer, majority side scales progressively).
+- This prevents abrupt jumps in layer cadence and makes transitions more predictable.
+
+### Mixed Filament Indexing And Mapping Fixes
+- Fixed mixed-filament row labeling so IDs stay compact after deletions in the Mixed Filaments panel.
+- Fixed regeneration order so auto-generated/precomputed mixes are appended at the end of existing mixed rows instead of being inserted at the front.
+- Fixed paint/index remapping when adding physical or virtual filaments so existing painted mixed regions keep their intended virtual filament mapping.
+- Fixed edge case where the first mixed filament could be temporarily replaced by a newly added physical filament.
+
+### Automatic Mixed Filaments Are Editable
+- Automatic mixed rows can now be expanded and edited through the gradient controls.
+- Edited auto-origin rows are treated as user-managed entries.
+- Deleting an edited auto-origin row now keeps that auto pair tombstoned (it will not be regenerated immediately and overwrite user intent).
+
+### Gradient Preview Color Fidelity
+- Updated gradient preview blending to use the FilamentMixer library path for color reproduction.
+- Preview swatches now better match expected mixed output.
+
+### Selective Expansion/Contraction Fix
+- Updated selective mixed-zone contraction so positive values trim only the outside-facing (visible) boundary band.
+- Internal/shared boundaries are no longer symmetrically contracted.
+- Outward expansion behavior remains unchanged.
+
+## Also Included (v0.91 Carry-Forward Fixes)
+- Windows startup/log path handling for non-ASCII usernames (UTF-8-safe path resolution).
+- Mixed-filament swatch desync/gray-regression fixes in preview rendering.
+
+## Internal/Config Changes
+- Removed `mixed_filament_cycle_layers` from config/UI wiring.
+- Extended mixed filament serialized metadata with auto-origin tracking to preserve delete/regenerate intent across reloads.
+- Added diagnostic logging around mixed-filament remap and selective-indentation application paths.
+
+## Important Notes
+- Experimental build with limited testing.
+- Some projects may show different gradient cadence behavior due to the removal of explicit layer-cycle control.
+- Use at your own risk.
+
+## Credits
+- FilamentMixer color blending integration is powered by FilamentMixer by [justinh-rahb](https://github.com/justinh-rahb).
+- Library: [https://github.com/justinh-rahb/filament-mixer](https://github.com/justinh-rahb/filament-mixer)