fix: add __-prefixed runtime primitives expected by El compiler

The El compiler generates calls to __-prefixed C primitives from within
El stdlib compiled code (e.g. __println, __str_len, __json_get, etc).
These were absent from el_runtime.c, causing linker failures when
building el-install, elb, or epm with the current compiler.

Add 46 __-prefixed aliases/implementations in el_runtime.c covering:
- I/O: __println, __print, __readline
- String: __str_len, __str_cmp, __str_ncmp, __str_alloc, __str_set_char,
  __str_concat_raw, __str_slice_raw, __str_char_at, plus numeric converters
- FS: __fs_read, __fs_write, __fs_exists, __fs_mkdir, __fs_list_raw, etc
- HTTP: __http_do, __http_do_map, __http_serve, __http_serve_v2,
  __http_response, __http_sse_* (weak stubs)
- JSON: __json_get, __json_set, __json_parse_map, __json_stringify_val, etc
- State, env, exec, uuid, sha256, args

lang/el-compiler/runtime/el_runtime.h

@@ -781,6 +781,93 @@ el_val_t emit_event(el_val_t name, el_val_t duration_ms);
 el_val_t __thread_create(el_val_t fn_name_v, el_val_t arg_v);
 el_val_t __thread_join(el_val_t tid_v);
 
+/* ── __ prefixed aliases (self-hosting compiler ABI) ─────────────────────────
+ * The El self-hosting compiler emits calls to __-prefixed names. These are
+ * forwarding wrappers around the existing el_runtime functions above.        */
+
+/* I/O */
+el_val_t  __println(el_val_t s);
+el_val_t  __print(el_val_t s);
+el_val_t  __readline(void);
+
+/* String */
+el_val_t  __int_to_str(el_val_t n);
+el_val_t  __str_to_int(el_val_t s);
+el_val_t  __float_to_str(el_val_t f);
+el_val_t  __str_to_float(el_val_t s);
+el_val_t  __str_len(el_val_t s);
+el_val_t  __str_char_at(el_val_t s, el_val_t i);
+el_val_t  __str_cmp(el_val_t a, el_val_t b);
+el_val_t  __str_ncmp(el_val_t a, el_val_t b, el_val_t n);
+el_val_t  __str_concat_raw(el_val_t a, el_val_t b);
+el_val_t  __str_slice_raw(el_val_t s, el_val_t start, el_val_t end);
+el_val_t  __str_alloc(el_val_t n);
+el_val_t  __str_set_char(el_val_t s, el_val_t i, el_val_t c);
+
+/* URL encoding */
+el_val_t  __url_encode(el_val_t s);
+el_val_t  __url_decode(el_val_t s);
+
+/* Environment */
+el_val_t  __env_get(el_val_t key);
+
+/* Subprocess */
+el_val_t  __exec(el_val_t cmd);
+el_val_t  __exec_bg(el_val_t cmd);
+
+/* Process */
+el_val_t  __exit_program(el_val_t code);
+
+/* Filesystem */
+el_val_t  __fs_exists(el_val_t path);
+el_val_t  __fs_mkdir(el_val_t path);
+el_val_t  __fs_read(el_val_t path);
+el_val_t  __fs_write(el_val_t path, el_val_t content);
+el_val_t  __fs_write_bytes(el_val_t path, el_val_t bytes, el_val_t n);
+el_val_t  __fs_list_raw(el_val_t path);
+
+/* HTTP server */
+el_val_t  __http_response(el_val_t status, el_val_t headers_json, el_val_t body);
+el_val_t  __http_serve(el_val_t port, el_val_t handler);
+el_val_t  __http_serve_v2(el_val_t port, el_val_t handler);
+
+/* HTTP conn fd / SSE (weak; overridden by el_seed.c when linked together) */
+el_val_t  __http_conn_fd(void);
+el_val_t  __http_sse_open(el_val_t conn_id);
+el_val_t  __http_sse_send(el_val_t conn_id, el_val_t data);
+el_val_t  __http_sse_close(el_val_t conn_id);
+
+/* HTTP client (requires HAVE_CURL; stubs provided for no-curl builds) */
+el_val_t  __http_do(el_val_t method, el_val_t url, el_val_t body,
+                    el_val_t headers_map, el_val_t timeout_ms);
+el_val_t  __http_do_map(el_val_t method, el_val_t url, el_val_t body,
+                        el_val_t headers_json, el_val_t timeout_ms);
+
+/* JSON */
+el_val_t  __json_array_get(el_val_t json, el_val_t index);
+el_val_t  __json_array_get_string(el_val_t json, el_val_t index);
+el_val_t  __json_array_len(el_val_t json);
+el_val_t  __json_get(el_val_t json, el_val_t key);
+el_val_t  __json_get_raw(el_val_t json, el_val_t key);
+el_val_t  __json_set(el_val_t json, el_val_t key, el_val_t value);
+el_val_t  __json_parse_map(el_val_t json_str);
+el_val_t  __json_stringify_val(el_val_t val);
+
+/* Hashing */
+el_val_t  __sha256_hex(el_val_t s);
+
+/* State K/V */
+el_val_t  __state_del(el_val_t key);
+el_val_t  __state_get(el_val_t key);
+el_val_t  __state_keys(void);
+el_val_t  __state_set(el_val_t key, el_val_t val);
+
+/* UUID */
+el_val_t  __uuid_v4(void);
+
+/* Args */
+el_val_t  __args_json(void);
+
 #ifdef __cplusplus
 }
 #endif