fix: make guardian names deterministic per floor instead of using Math.random()

- generateGuardianName() now takes a floor parameter and uses floor % prefixes.length for deterministic prefix selection
- generateComboGuardianName() now takes a floor parameter and uses (floor + i) % prefixes.length for each element
- getGuardianForFloor() passes floor to generateGuardianName for static guardians with empty names
- getExtendedGuardian() passes floor to generateComboGuardianName for combo guardians
- Removes dependency on Math.random() → names are stable across ticks/refreshes

Fixes #161

docs/dependency-graph.json

@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated": "2026-05-27T09:16:36.915Z",
+    "generated": "2026-05-27T09:18:35.464Z",
     "description": "Import dependency graph for src/lib/game. Keys are files, values are arrays of files they import.",
     "usage": "To find what a file affects, search for its path in the VALUES. To find what a file depends on, look at its KEY entry."
   },