Prepare 12.1.0

[zeriyoshi]

• [Electron] Improved GUI responsiveness
• [Electron] PNG: Added option to multithreading (palette256)
• [Electron] Added auto-update check when resetting settings
• [Electron] Fundamentally restructured the GUI again
• [Electron] Improved overall performance with SIMD
• [Electron / Chrome] Added display of conversion time in milliseconds
• [Electron / Chrome] Added cancel conversion fucntion in progress
• and more

[Copilot]

Pull request overview

This pull request introduces multi-threaded image processing support across the Colopresso library and applications (Electron/Chrome), fundamentally restructuring the GUI architecture for improved responsiveness and performance. The changes add pthreads support for C code, Rayon thread pools for Rust bridge code, and implement a web worker-based conversion architecture for the frontend.

Key changes:

• Added cross-platform threading support (pthreads on Unix/macOS, Windows Thread API wrapper on Windows, Emscripten pthreads for WASM)
• Implemented parallel processing for CPU-intensive PNG operations (bit-depth reduction, palette quantization)
• Restructured GUI to use web workers for non-blocking conversions with cancellation support
• Added WASM separation mode for stable Rust builds (Chrome Extension/Electron without native threads)

Reviewed changes

Copilot reviewed 68 out of 70 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
library/src/thread.c	New file implementing parallel_for with pthread-based thread pool for C code
library/src/portable.c	Added Windows thread API wrapper (pthread compatibility layer)
library/src/pngx_reduced.c	Parallelized bitdepth reduction and color quantization operations
library/src/pngx_palette256.c	Added prepare/finalize API for separated WASM quantization workflow
library/src/pngx_limited.c	Parallelized limited4444 bitdepth reduction
library/src/pngx_common.c	Parallelized snap_rgba_image_to_bits operation
library/pngx_bridge/src/lib.rs	Implemented thread pool caching for Rayon, added WASM-bindgen support
library/pngx_bridge/src/wasm.rs	New WASM module with separate quantization/optimization APIs
library/pngx_bridge/Cargo.toml	Added optional rayon and wasm-bindgen features
cmake/threads.cmake	New CMake module for cross-platform thread configuration
cmake/pngx_bridge_wasm.cmake	Build system for separate WASM bridge module
app/shared/core/conversionWorker.ts	New web worker for background image conversion
app/shared/core/conversionWorkerClient.ts	Client interface for worker communication
app/shared/core/pngxBridge.ts	TypeScript bindings for WASM-separated pngx_bridge
app/electron/main.ts	Added cross-origin isolation for SharedArrayBuffer support

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