Neon3 v0.2.12 — multi-language editor + LSP introspection + persistent editor endpoint

v0.2.12

• editor-runtime: editor.document.open accepts nui_flow/typescript/rust/cpp (tree-sitter tokenize)
• 6 new LSP RPCs: diagnostics / hover / definition / references / symbols / signature_help (rust-analyzer, typescript-language-server, clangd; env-overridable NEON3_LSP_*)
• LSP is best-effort: missing server degrades to server_unavailable, never blocks editing
• fix: editor-runtime now serves on a persistent multiplexing connection (BlockingRpcServer) — SDK long-lived clients no longer hit closed sockets after the first RPC
• editor kernel: LspClient diagnostics collection + hover/definition/references/symbols/signature_help, request timeouts, fast-fail on missing server binaries