Add selection validation and improve tooltip component

- Add validation system to prevent contradicting conditions:
  - Same entity in include/exclude detection
  - Parent-child conflict detection for tree entities
  - Redundant selection prevention
  - Toast notifications for validation errors

- Fix entity icons (employees: briefcase, taxes: calculator)

- Improve tooltip component:
  - Use Material Icons instead of broken FA4 icons
  - Fix positioning using getBoundingClientRect for viewport coords
  - Add click-to-pin functionality with close button
  - Pinned tooltips show X icon and close button in corner

- Add lightweight test suite (31 tests) for validation logic

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -8,7 +8,8 @@
     "build:js": "gulp js",
     "watch": "gulp watch",
     "watch:css": "gulp watch:scss",
-    "watch:js": "gulp watch:js"
+    "watch:js": "gulp watch:js",
+    "test": "node tests/run-tests.js"
   },
   "devDependencies": {
     "gulp": "^4.0.2",
@@ -17,6 +18,8 @@
     "gulp-sass": "^5.1.0",
     "gulp-sourcemaps": "^3.0.0",
     "gulp-terser": "^2.1.0",
+    "jquery": "^3.7.1",
+    "jsdom": "^22.1.0",
     "sass": "^1.63.6"
   }
 }