Unify release workflows and fix macOS installer

- Build WASM with platform binaries, release together
- Fix install.sh: auto-detect version, handle zstd/SDK deps
- Add macOS prerequisites to README

remove clangd download from deploy-playground.yml

remove clangd download from deploy-playground.yml

Update build-clang.yml

remove windows build while I debug issues with the windows build, so that the linux and mac builds can succeed and create artifacts

Update build-clang.yml

remove windows build while I debug issues with the windows build, so that the linux and mac builds can succeed and create artifacts

Fix deployment workflow and add clangd build

Changes to build workflow:
- Build both clang and clangd WASM (clang-tools-extra enabled)
- Include clangd files in release for LSP features

Changes to deploy workflow:
- Download WASM to /tmp first to avoid git checkout conflicts
- Copy WASM files after checking out gh-pages branch
- Fixes error: 'Your local changes would be overwritten by checkout'

Fix CI: add llvm-config to build and disable Jekyll in gh-pages

Fix deployment workflow and add clangd build

Changes to build workflow:
- Build both clang and clangd WASM (clang-tools-extra enabled)
- Include clangd files in release for LSP features

Changes to deploy workflow:
- Download WASM to /tmp first to avoid git checkout conflicts
- Copy WASM files after checking out gh-pages branch
- Fixes error: 'Your local changes would be overwritten by checkout'

Fix CI: add llvm-config to build and disable Jekyll in gh-pages

Optimize CI test workflow with caching

- Add ccache to speed up C++ compilation (2-10x faster rebuilds)
- Cache build directory between runs
- Cache key based on source file hashes (rebuilds only when code changes)
- Use LLVM_OPTIMIZED_TABLEGEN for faster initial builds
- First run: ~30-40 mins
- Subsequent runs with no changes: ~2-5 mins (just cache restore + test)
- Subsequent runs with small changes: ~5-10 mins (incremental build)

This makes the CI actually usable for regular development!