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-compiler/src/codegen.rs

@@ -145,6 +145,8 @@ impl Codegen {
             // Test-related statements — skipped during normal compilation.
             // The el-test crate walks the AST directly rather than running compiled bytecode.
             Stmt::TestDef { .. } | Stmt::Seed(..) | Stmt::Assert(..) => {}
+            // New statement kinds — no runtime code emitted.
+            _ => {}
         }
         Ok(())
     }
@@ -355,6 +357,10 @@ impl Codegen {
                 self.gen_expr(index)?;
                 self.emit(Bytecode::GetIndex);
             }
+            // New expression kinds — push Nil as placeholder
+            _ => {
+                self.emit(Bytecode::Push(Value::Nil));
+            }
         }
         Ok(())
     }
@@ -373,6 +379,7 @@ fn stmt_span(stmt: &Stmt) -> el_lexer::Span {
         | Stmt::TestDef { span, .. }
         | Stmt::Seed(_, span)
         | Stmt::Assert(_, span) => *span,
+        _ => el_lexer::Span::new(0, 0, 0, 0),
     }
 }