fix: ensure procedural guardian names are unique across floors

- Modified generateGuardianName() in guardian-encounters.ts to add a cycleOffset (floor/50) that shifts prefix selection for the same elements at different 100-floor ranges
- For multi-element names, also shift the title by cycleOffset to further reduce collision chance
- Added regression test guardian-names-unique.test.ts with 7 test cases covering:
  * Previously colliding floors (170/370 crystal, 200/230 exotic convergence, 210/240 astral convergence)
  * All static guardian floors (10-240) uniqueness
  * All procedural guardian floors (250-490) uniqueness
  * Full range (10-490) uniqueness
  * Determinism check
  * Title format validation

Fixes #376

docs/dependency-graph.json

@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated": "2026-06-12T07:05:50.633Z",
+    "generated": "2026-06-12T07:45:30.561Z",
     "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."
   },