fix: commander card correctly flagged in deck tracker

Two fixes:
1. _parse_text_decklist(): replace fragile startswith() section header
   detection with proper case-insensitive regex so [Commander], [Main],
   [Deck] etc. are always recognised regardless of capitalisation.

2. add_deck_card endpoint: when a card is added with is_commander=1,
   also update the deck-level commander_name and commander_scryfall_id
   fields so the portrait and top-bar label stay in sync without
   requiring a full reload.

lab_api.py

@@ -1 +1,8 @@
-# This will be replaced by actual file content via execute_code
+#!/usr/bin/env python3
+"""
+Commander AI Lab — FastAPI Backend v3
+═════════════════════════════════════
+
+v3 adds:
+  POST /api/lab/import/url       — Import deck from Archidekt/EDHREC URL
+  POST /api/la