refactor(lsp): centralize protocol runtime

[hongjr03]

Summary

• add a shared vide-lsp-runtime crate for typed routing, request lifecycle, cancellation, retry, response encoding, and in-memory transport
• route native and browser/WASM sessions through one protocol registry
• remove the legacy dispatcher modules, duplicate request queues, cancellation plumbing, and trace wrapper without compatibility shims
• document the new runtime seam and transport responsibilities

Verification

• cargo test --workspace -- --test-threads=1 (540 passed, 3 ignored)
• cargo check -p vide-lsp-runtime --target wasm32-unknown-emscripten
• cargo check -p vide-lsp-wasm
• native stdio smoke: initialize → shutdown → exit 0
• browser JSON smoke: initialize → shutdown

Notes

• production Rust LOC is net -1: application-layer code is reduced by 418 lines and replaced by a 417-line shared runtime
• the full Emscripten bundle command reaches the existing slang C++ build but cannot complete on this machine because Homebrew Emscripten 4.0.22 does not provide clang-scan-deps; the runtime itself passes the Emscripten target check

[github-actions]

Docs preview: https://vide.pascal-lab.net/preview/pr-320/