fix(client): address PR #109 review — 6 warnings + 5 suggestions

Star map (W1-W3, S3):
- _process visibility guard + dirty flag (no redraw when hidden/unchanged)
- _system_hash masked to 31-bit positive range
- Extracted _find_nearest_system() shared helper

game_state.gd (W4):
- Inline load() in apply_snapshot() replaces per-tick overhead; safe at
  runtime because script is already in resource cache

Data pipeline (W5-W6):
- Script-relative path resolution via __file__
- --check mode + make check-star-map staleness target

Minor (S1-S2, S5):
- Removed redundant bone_idx assignment
- Simplified double-negative test assertion
- Documented autoload parse-order convention in CLAUDE.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/data/star_map_data.json

@@ -1,6 +1,6 @@
 {
   "_meta": {
-    "generated_from": "docs/design/star-map.json + server/data/systems.db",
+    "generated_from": "star-map.json + systems.db",
     "system_count": 301,
     "edge_count": 335,
     "note": "Client-side star map data. Regenerate with: tooling/generate-star-map-data.py"
@@ -4360,4 +4360,4 @@
       "GJ 71"
     ]
   ]
-}
+}