fix(simulation): address PR #87 review — name collision, validation, and polish

- Fix critical name collision: shuffle+pop for unique NPC names (#3)
- Validate population_density >= 1 in generator and validator (#4)
- Guard against empty given_names/roles with validator warnings (#5)
- Extract filler word cap to MAX_FILLER_WORDS constant (#6)
- Fix cultural behavior gate checking wrong field (#7)
- Document intentional one-directional relationships (#8)
- Validate min_npcs <= max_npcs in validator (#9)
- Fix validate-ron script realpath error handling (#10)
- Add TODO comments for spike-specific code duplication (#11, #12, #13)

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

tooling/validate-ron

@@ -20,7 +20,12 @@ if [ $# -lt 2 ]; then
     exit 1
 fi
 
-# Resolve file to absolute path before changing directory
+# Check file exists before resolving — realpath gives unhelpful errors otherwise
+if [ ! -f "$1" ]; then
+    echo "Error: file not found: $1"
+    exit 1
+fi
+
 FILE="$(realpath "$1")"
 SCHEMA="$2"