Add Blackjack game: rules, card rendering, game loop and tests

Implement the playable console game for gateway MIL-002.

- rules.py: deal_card, calculate_score (blackjack = 0, aces drop 11 ->
  1)
  and compare with an Outcome enum; no console I/O
- display.py: hand rendering as plain-text rank plus suit emoji (keycap
  emoji rendered as boxes in common terminals), score formatting and
  outcome messages
- art.py: course logo shown at the start of every game
- game.py: play_game (hit/stand, dealer draws below 17), play (restart
  loop, console clear, logo) and ask_yes_no with re-prompt; read, write
  and draw are injected so games can be scripted
- __main__.py: python -m blackjack entry point, exits cleanly on
  Ctrl+C/Ctrl+D
- constants.py: card ranks and suits, prompts and messages
- tests: 32 new unit and scripted end-to-end tests (35 in total)
- README: run instructions for python -m blackjack

Closes #7
Closes #8
Closes #9
Closes #10
Closes #11
Closes #12
Closes #13
Closes #14

Task: MIL-002#1
Task: MIL-002#2
Task: MIL-002#3
Task: MIL-002#4
Task: MIL-002#5
Task: MIL-002#6
Task: MIL-002#7
Task: MIL-002#8

src/blackjack/__main__.py

@@ -0,0 +1,21 @@
+"""!
+@file __main__.py
+@brief Entry point: python -m blackjack.
+"""
+
+from blackjack.constants import MESSAGE_GOODBYE
+from blackjack.game import play
+
+
+def main() -> None:
+    """!
+    @brief Run the game; leave quietly on Ctrl+C or Ctrl+D.
+    """
+    try:
+        play()
+    except (EOFError, KeyboardInterrupt):
+        print(f"\n{MESSAGE_GOODBYE}")
+
+
+if __name__ == "__main__":
+    main()