feat(coords): Chunk-Namen als Planquadrat A1 bis L12

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/fixtures/chunk-names.json

@@ -0,0 +1,5 @@
+{
+  "pairs": [["A1", 0, 0], ["L1", 11, 0], ["A12", 0, 11], ["L12", 11, 11], ["C10", 2, 9]],
+  "lowercase": [["c10", 2, 9], ["l12", 11, 11]],
+  "invalid": ["M1", "A0", "A13", "A", "10", "", "A01", "B-3", " "]
+}