feat: integrate playground into workspace

[hongjr03]

Summary

This change brings the playground into the Vizsla repository as first-class workspace code instead of maintaining a separate patched consumer. The Rust WASM entry point now lives under crates/vizsla-lsp-wasm, the frontend lives under playground, and the docs site imports the playground package directly instead of committing generated docs/public/vizsla-lab assets.

Playground Architecture

flowchart LR
    subgraph Browser[Browser runtime]
        Component["<vizsla-lab> web component"]
        Monaco["Monaco editor + scenarios"]
        Client["Browser LSP client"]
        Worker["vizsla-lsp.worker"]
    end

    subgraph Wasm[WASM package]
        Adapter["JS FFI adapter"]
        Ffi["C ABI exports"]
        Server["vizsla::browser::BrowserServer"]
    end

    subgraph Core[Core Vizsla crate]
        State["GlobalState + main-loop event drain"]
        Vfs["browser VFS notification bridge"]
        Analysis["existing config, resolver, diagnostics"]
    end

    Component --> Monaco
    Monaco --> Client
    Client <--> Worker
    Worker <--> Adapter
    Adapter <--> Ffi
    Ffi <--> Server
    Server <--> State
    State <--> Vfs
    State --> Analysis

Loading

The important boundary is that the WASM crate is now a thin FFI layer. It no longer path-includes private source files from the main crate; browser-specific LSP handling is exposed through vizsla::browser::BrowserServer, so the playground uses the same analysis code through a real crate API.

Other Changes

• Move Emscripten setup into CI through a pinned local composite action, while local npm run build:wasm consumes an already activated SDK.
• Remove the old standalone playground patch/vendor/version-lock machinery.
• Wire the docs build to copy only generated WASM assets needed at build time.
• Keep VS Code grammar and language configuration sourced from the repository instead of duplicated playground assets.

Validation

• rustup run nightly cargo fmt --all -- --check
• rustup run nightly cargo check -p vizsla-lsp-wasm
• rustup run nightly cargo clippy -p vizsla -p vizsla-lsp-wasm --all-targets -- -D warnings
• npm ci in playground
• npm run build:wasm in playground
• npm run build:embed in playground
• npm run build in playground
• npm ci in docs
• npm run build in docs

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-160/