Dev (#296)

* feat(info-bar): display Mode R status and unique pairs count

* fix(raster): auto-switch to compatible dithering mode when enabling raster

* feat: allow drag-drop to replace existing source image

- Add dropzone wrapper around ImageSelector in source-section.tsx
- Reset adjustments and selection when replacing image via drop
- Add data-testid to ImageUpload for testing
- Add tests for drop functionality (image processing and non-image rejection)

* fix(source-selector): allow selection drag outside container bounds

- Replace react-dropzone with native drop events in source-section to avoid
  conflicts with ImageSelector's internal drag operations
- Use window mousemove/mouseup events during drag to track cursor position
  even when it moves outside the selector container
- Add containerRef to SourceSelectorView for coordinate calculations
- Fixes issue where selection rectangle couldn't be positioned at image edges

* perf: optimize CPC Plus color analysis with O(1) lookup

- Add getCPCPlusPaletteIndex() for direct palette index lookup
- Reduces frequency analysis from 744ms to 0.4ms (~1800x faster)
- Clean up verbose debug logs in color selection helpers
- Add targeted timing logs for workingImageAtom and dithering
- Refactor useImageAdjustement with refs to reduce rerenders

* feat(dithering): add Ostromoukhov and Blue Noise algorithms

- Add Ostromoukhov error diffusion with variable coefficients (256 levels)
- Implement serpentine scan pattern for better artifact reduction
- Add EGX support for Ostromoukhov dithering
- Add Mode R support for Ostromoukhov and Blue Noise
- Add 64x64 Blue Noise texture for threshold-based dithering
- Fix missing Ostromoukhov coefficients (indices 126-127)
- Add fallback protection for undefined coefficients

* chore: fix linting warnings

- Replace Object.assign with spread operator
- Replace Array() with new Array()
- Replace window with globalThis for SSR compatibility
- Replace global with globalThis
- Extract nested ternary operations into helper functions
- Fix negated conditions (swap branches)
- Remove unnecessary type assertions
- Use CpcMode type alias instead of inline union
- Fix inverted condition in optimize-line-palettes
- Use 1 instead of 1.0 for integer values

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Co-authored-by: Ivan Duchauffour <iduchauffour@welcomr.com>

Author: IIIvan37