feat(dashboard): hand-rolled Rhai parser + symbol table + Vitest

Foundation for upcoming editor features (scope-aware autocomplete,
goto-def / find-usages, source formatter). Hand-rolled recursive
descent in TypeScript with Pratt precedence climbing for expressions,
error-tolerant so partial trees stay usable while the user is typing.
Symbol table walks the AST to produce per-scope declarations, usage
sites, and object-literal field maps. Vitest added as a dev-only
runner; no editor wiring in this commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dashboard/package.json

@@ -10,7 +10,8 @@
     "check": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json",
     "check:watch": "svelte-kit sync && svelte-check --tsconfig ./tsconfig.json --watch",
     "format": "prettier --write .",
-    "lint": "prettier --check . && eslint ."
+    "lint": "prettier --check . && eslint .",
+    "test": "vitest run"
   },
   "devDependencies": {
     "@eslint/js": "^9.18.0",
@@ -28,7 +29,8 @@
     "svelte-check": "^4.1.4",
     "typescript": "^5.7.3",
     "typescript-eslint": "^8.20.0",
-    "vite": "^6.0.7"
+    "vite": "^6.0.7",
+    "vitest": "^3.0.5"
   },
   "overrides": {
     "cookie": "^0.7.2"