Add server-side builtins, import system, and http_serve for Neuron Code rewrite

- Import resolution: resolve_imports() pre-processes import statements by
  reading and concatenating referenced .el files before compilation
- http_serve builtin: tiny_http-based server on configurable port; POST
  /axon/message stores request in __request__ state, invokes handle_request
  entry point via sub-interpreter, reads __response__ state for reply
- New builtins: blake3_hash, uuid_new, fs_list_recursive, fs_mkdir, fs_exists,
  path_join, path_parent, str_trim, str_contains, str_replace, str_starts_with,
  str_ends_with, str_last_index_of, json_get, json_array_push, json_array_len,
  now_millis, http_get, http_post, int_to_str
- Catch-all arms in el-types and el-compiler for new AST variants (Import,
  ProtocolDef, ImplDef, Closure, Try, MapLiteral, TypeExpr::Result, TypeExpr::Map)
- Parser: decorators field on FnDef, import/protocol/impl parsing

crates/el-parser/src/ast.rs

@@ -55,6 +55,10 @@ pub enum TypeExpr {
     Optional(Box<TypeExpr>),
     /// A function type: `fn(A, B) -> C`
     Fn { params: Vec<TypeExpr>, return_type: Box<TypeExpr> },
+    /// `Result<T, E>` — built-in error-propagation type
+    Result { ok: Box<TypeExpr>, err: Box<TypeExpr> },
+    /// `Map<K, V>` — built-in key-value map type
+    Map { key: Box<TypeExpr>, value: Box<TypeExpr> },
 }
 
 // ── Patterns (for match arms) ─────────────────────────────────────────────────
@@ -103,6 +107,17 @@ pub enum Expr {
     Path { segments: Vec<String> },
     /// Index expression: `arr[0]`
     Index { object: Box<Expr>, index: Box<Expr> },
+    /// Closure: `|x: Int| x * 2` or `|x: Int| -> Int { x * 2 }`
+    Closure {
+        params: Vec<Param>,
+        return_type: Option<TypeExpr>,
+        body: Box<Expr>,
+        span: Span,
+    },
+    /// Try operator: `expr?` — unwraps Result, propagates error
+    Try(Box<Expr>),
+    /// Map literal: `{"key": value, ...}`
+    MapLiteral(Vec<(Expr, Expr)>),
 }
 
 // ── Match arm ─────────────────────────────────────────────────────────────────
@@ -114,6 +129,27 @@ pub struct MatchArm {
     pub span: Span,
 }
 
+// ── Decorators ────────────────────────────────────────────────────────────────
+
+/// A decorator applied to a function: `@name` or `@name(args)`
+#[derive(Debug, Clone, PartialEq)]
+pub struct Decorator {
+    pub name: String,
+    pub args: Vec<Expr>,
+    pub span: Span,
+}
+
+// ── Protocol ──────────────────────────────────────────────────────────────────
+
+/// A method signature inside a protocol definition.
+#[derive(Debug, Clone, PartialEq)]
+pub struct ProtocolMethod {
+    pub name: String,
+    pub params: Vec<Param>,
+    pub return_type: TypeExpr,
+    pub span: Span,
+}
+
 // ── Statements ────────────────────────────────────────────────────────────────
 
 /// A named parameter in a function definition.
@@ -154,9 +190,10 @@ pub enum Stmt {
     Return(Expr, Span),
     /// A bare expression used as a statement (usually a call).
     Expr(Expr, Span),
-    /// `fn name(params) -> ReturnType { body }`
+    /// `fn name(params) -> ReturnType { body }` (with optional decorators)
     FnDef {
         name: String,
+        decorators: Vec<Decorator>,
         params: Vec<Param>,
         return_type: TypeExpr,
         body: Vec<Stmt>,
@@ -185,6 +222,26 @@ pub enum Stmt {
     Seed(SeedStmt, Span),
     /// `assert <expr>`
     Assert(Expr, Span),
+    /// `import std::collections::Map` or `from pkg import { A, B }`
+    Import {
+        path: Vec<String>,
+        names: Vec<String>,
+        alias: Option<String>,
+        span: Span,
+    },
+    /// `protocol Name { method sigs... }`
+    ProtocolDef {
+        name: String,
+        methods: Vec<ProtocolMethod>,
+        span: Span,
+    },
+    /// `impl Protocol for TypeName { fn ... }`
+    ImplDef {
+        protocol_name: String,
+        type_name: String,
+        methods: Vec<Stmt>,
+        span: Span,
+    },
 }
 
 // ── Top-level program ─────────────────────────────────────────────────────────