docs: add guided offline map install steps

tests/build_scripts/test_map_web_installer_contract.py

@@ -27,6 +27,24 @@ def test_map_installer_ui_is_local_file_to_sd_and_offline_only() -> None:
     assert "Map data (c) OpenStreetMap contributors" in source
 
 
+def test_map_installer_explains_the_complete_sd_card_workflow() -> None:
+    source = FLASHER.read_text(encoding="utf-8")
+    assert '<ol class="map-install-steps">' in source
+    assert (
+        'href="https://download.tiles.coalition.space/" '
+        'target="_blank" rel="noopener noreferrer"'
+    ) in source
+    expected_steps = (
+        "Download a compatible MUI map ZIP",
+        "Turn the T-Deck off",
+        "Choose the downloaded ZIP",
+        "Click <strong>Install and Enable</strong>",
+        "Safely eject the SD card",
+    )
+    positions = [source.index(step) for step in expected_steps]
+    assert positions == sorted(positions)
+
+
 def test_map_installer_has_no_tile_network_fetch_path() -> None:
     source = INSTALLER.read_text(encoding="utf-8").lower()
     for forbidden in ("fetch(", "xmlhttprequest", "websocket", "http://", "https://"):