chore(meta): add development cascade to CLAUDE.md + vendor/ to gitignore

6-phase cascade: wiki content → economics → planetary maps → player
control → world gen → detail coloring. Each phase completes before
the next begins. Agents must not discuss detail from later phases.

vendor/ added to .gitignore for cloned reference repos (8 Godot
plugins for world generation research).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -30,6 +30,9 @@ spikes/**/*.uid
 # Asset downloads (vendor archives, not game content)
 docs/assets/downloads/
 
+# Reference repos for investigation
+vendor/
+
 # Database (shared across worktrees at ../settledreach.db, not tracked)
 db/commonwealth.db*