runtime: add dharma-required functions to el_runtime.c and runtime/*.el

Add the following functions that dharma registry calls but were missing
from the El runtime:

el_runtime.c (consumed by the old build system via released SDK):
  - list_len, list_get — aliases for el_list_len/el_list_get (handlers.el)
  - json_array_push — append pre-encoded element to JSON array string
  - now_millis, unix_timestamp_ms, time_now_ms — ms-since-epoch aliases
  - log_info, log_warn — structured stderr log helpers
  - config — reads config from environment (alias for getenv)
  - http_patch — HTTP PATCH with Content-Type: application/json
  - http_post_engram — HTTP POST with optional X-API-Key header
  - http_get_engram — HTTP GET with optional X-API-Key header
  - str_to_bytes — encode string as JSON byte array [72,101,...]
  - bytes_to_str — decode JSON byte array back to string
  - hash_sha256 — SHA-256 hex digest using built-in sha256 impl

runtime/*.el (consumed by the new build system):
  - http.el: http_patch, http_post_engram, http_get_engram
  - time.el: now_millis, unix_timestamp_ms, time_now_ms
  - env.el: config, log_info, log_warn, list_len, list_get
  - json.el: json_array_push, bytes_to_str
  - string.el: str_to_bytes, hash_sha256 (via __sha256_hex seed)

el_seed.h / el_seed.c:
  - __sha256_hex primitive with self-contained SHA-256 implementation

runtime/env.el

@@ -63,6 +63,34 @@ fn state_keys() -> String {
     return __state_keys()
 }
 
+// ── DHARMA runtime helpers ─────────────────────────────────────────────────
+
+// config — read a configuration value from the environment.
+// Returns "" if the variable is not set. Alias for env().
+fn config(key: String) -> String {
+    return __env_get(key)
+}
+
+// log_info — write an [INFO] log line to stdout.
+fn log_info(msg: String) {
+    __println("[INFO] " + msg)
+}
+
+// log_warn — write a [WARN] log line to stdout.
+fn log_warn(msg: String) {
+    __println("[WARN] " + msg)
+}
+
+// list_len — return the number of elements in a list. Alias for el_list_len.
+fn list_len(lst: [String]) -> Int {
+    return el_list_len(lst)
+}
+
+// list_get — return the element at index i in a list. Alias for el_list_get.
+fn list_get(lst: [String], i: Int) -> String {
+    return el_list_get(lst, i)
+}
+
 // ── UUID generation ────────────────────────────────────────────────────────
 
 // uuid_new — generate a new random UUID v4.