Bundle WASM-only image codec runtimes

[343dev]

Replace the platform-specific Sharp, Guetzli, and Gifsicle binaries with WebAssembly runtimes bundled with Optimizt.

This PR also converts the repository to npm workspaces. Each codec runtime can now be built, verified, and vendored independently. Only @343dev/optimizt is published.

User-facing changes

• Sharp, Guetzli, and Gifsicle now use WebAssembly runtimes bundled with Optimizt.
• Wasm64 lets Guetzli process JPEG files beyond the 4 GiB wasm32 address-space limit.
• GIF optimization now rejects encoded inputs larger than 128 MiB.
• GIF optimization now rejects images with more than 100,000 frames.
• GIF optimization now rejects images whose canvas area exceeds 134,217,728 pixels.
• GIF optimization now rejects images whose total frame area exceeds 134,217,728 pixels.
• Optimizt can now terminate Gifsicle operations when a run is interrupted.
• This PR updates the CLI option descriptions and migration documentation.

Breaking changes

• Optimizt now requires Node.js 24.0.0 or newer.
• The bundled Guetzli and Gifsicle runtimes require WebAssembly memory64.
• Optimizt no longer installs platform-specific Sharp binaries.
• Optimizt rejects GIF files that exceed the new safety limits.

Implementation

• Move the CLI to the packages/optimizt workspace.
• Add private workspaces for the Sharp, Guetzli, and Gifsicle runtimes.
• Vendor the generated codec distributions in the published Optimizt package.
• Pin and verify the upstream sources and build toolchains.
• Add native-parity fixtures and verification tests for Guetzli and Gifsicle.
• Add package-content tests that verify all required vendored files are published.
• Update the Docker and CI workflows to use the workspace-based build.

Compatibility

The existing Optimizt CLI and configuration format remain unchanged. Parity tests compare each codec's output with the corresponding native implementation.