add El LSP skeleton — language server, VSCode extension, syntax highlighting

Implements a Language Server Protocol server for El files over stdin/stdout
JSON-RPC. Provides completions (builtins + keywords + document functions),
hover documentation, go-to-definition, and full document sync.

Also adds a VSCode extension that launches the binary as a child process and
a TextMate grammar for .el syntax highlighting.

NOTE: el-lsp.el calls __read_n(n: Int) -> String, a seed primitive not yet
in el_runtime.c. Build.sh documents the required C implementation; the seed
agent must add it before the binary will link.

tools/lsp/vscode-extension/language-configuration.json

@@ -0,0 +1,26 @@
+{
+  "comments": {
+    "lineComment": "//"
+  },
+  "brackets": [
+    ["{", "}"],
+    ["[", "]"],
+    ["(", ")"]
+  ],
+  "autoClosingPairs": [
+    { "open": "{", "close": "}" },
+    { "open": "[", "close": "]" },
+    { "open": "(", "close": ")" },
+    { "open": "\"", "close": "\"", "notIn": ["string"] }
+  ],
+  "surroundingPairs": [
+    ["{", "}"],
+    ["[", "]"],
+    ["(", ")"],
+    ["\"", "\""]
+  ],
+  "indentationRules": {
+    "increaseIndentPattern": "\\{[^}]*$",
+    "decreaseIndentPattern": "^\\s*}"
+  }
+}