Add random scenario and refactor case handling

Consolidate scenario creation by replacing separate normal/edge/clear handlers with createCase({withWalls, scenario}). Add a new 'random' scenario that picks random start/end positions and places random walls (controlled by MAX_RANDOM_WALLS_FACTORS). Change pathLength to a string and display "∞" for empty paths. Update applyGridSize logic to avoid unnecessary resets when dimensions unchanged and to initialize with the new API. Add random helper and MAX_RANDOM_WALLS_FACTORS constant, update template buttons to call createCase, and add i18n entries for the random case and updated clear-board label.

src/assets/i18n/de.json

@@ -303,7 +303,8 @@
     "ASTAR": "Start A*",
     "NORMAL_CASE": "Testaufbau",
     "EDGE_CASE": "A* Grenzfall-Aufbau",
-    "CLEAR_BOARD": "Board leeren",
+    "RANDOM_CASE": "Zufälliger-Aufbau",
+    "CLEAR_BOARD": "Leeres Gitter",
     "VISITED": "Besucht",
     "PATH": "Pfad",
     "PATH_LENGTH": "Pfadlänge",