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/string.el

@@ -876,3 +876,32 @@ fn str_join(parts: [String], sep: String) -> String {
     }
     return result
 }
+
+// ── DHARMA byte encoding (str_to_bytes) ──────────────────────────────────────
+//
+// str_to_bytes — encode a string as a JSON array of unsigned byte values.
+// "hi" -> "[104,105]"
+// Used by db.el to store content in Engram JSON nodes as a byte array.
+// Note: bytes_to_str (the inverse) is defined in json.el because it depends
+// on json_array_get_string which is defined there.
+fn str_to_bytes(s: String) -> String {
+    let n: Int = __str_len(s)
+    if n == 0 { return "[]" }
+    let result: String = "["
+    let i: Int = 0
+    while i < n {
+        let b: Int = __str_char_at(s, i)
+        if i > 0 { result = __str_concat_raw(result, ",") }
+        result = __str_concat_raw(result, __int_to_str(b))
+        i = i + 1
+    }
+    return __str_concat_raw(result, "]")
+}
+
+// ── Cryptographic hashing ─────────────────────────────────────────────────────
+
+// hash_sha256 — return the SHA-256 hex digest of a string.
+// Delegates to the __sha256_hex seed primitive.
+fn hash_sha256(s: String) -> String {
+    return __sha256_hex(s)
+}