feat: add ai agent http agent

texas_holdem/prompts/game_start.md

@@ -0,0 +1,22 @@
+# GAME_START
+
+A new hand of Texas Hold'em is about to begin. Use this snapshot as the
+fresh context for every decision in the upcoming hand. Hole cards and
+betting state from prior hands are NOT carried over.
+
+## Table
+
+- Game id: {game_id}
+- Hand number: {hand_number}
+- Status: {status}
+- Blinds: small={small_blind}, big={big_blind}
+- Button seat: {button_seat}
+- Starting stack: {starting_stack}
+
+## Players (current stacks)
+
+{players_block}
+
+## Hands played so far ({hand_count})
+
+{history_block}