refactor: decompose god-classes, add lint gates, restructure packages

- Decompose all 11 god-classes (>200 lines) into facade + collaborators
  (command/, schematic/, config/, generator/, mode/, papi/, adaptive/,
  storage/, player/, leaderboard/) — every file is now <=200 lines
- Add PMD 7 (report-only) + stricter checkstyle rules (NPath, IllegalCatch,
  NestedDepth, Whitespace, MissingOverride); fix real bugs found
  (printStackTrace, resource leaks in ConfigLoader/SQLStatsStorage)
- docs/ARCHITECTURE.md: target structure + 'one folder = one purpose' rule
- Pilot restructure: command/core|util/, mode/impl/solo|multi|barrier/,
  hook/papi/resolver/; cross-package classes made public
- TODO.md: track warning cleanup (132-138) + restructure progress

.gitignore

@@ -72,3 +72,6 @@ TODO.md
 
 # Compiled output
 bin/
+
+# Reference material (local only)
+ref/