test: add Vitest and Phase 1 pure-helper suite

Introduce automated testing to a project that had no test runner, no
test script and no CI. Vitest fits the existing Vite setup with near-zero
config; a standalone vitest.config.ts wires the @/ alias via
vite-tsconfig-paths and runs in the node environment, avoiding the app's
Tailwind/React/WASM plugins that pure-logic tests do not need.

Cover the cheapest, highest-value surface first: pure helpers with no DOM,
WASM or database. getNextSequence and cloneField (field.ts), the
charset/collation and SQLite integer-column reordering plus enum naming
(render-uttils.ts), and orderTables including the CircularDependencyError
cycle path that backs the Foreign Key Cycle Detection feature.

The build's tsc step is unaffected (plain tsc no-ops on the root config)
and the new files typecheck clean under strict and lint clean.

package.json

@@ -7,7 +7,9 @@
     "dev": "vite",
     "build": "tsc && cross-env NODE_OPTIONS=--max-old-space-size=8192 vite build",
     "lint": "eslint -c .eslintrc.json ./src/**/**/*.{ts,tsx} --fix",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@codemirror/lang-sql": "^6.9.0",
@@ -105,6 +107,7 @@
     "typescript": "5.6.3",
     "vite": "^5.2.0",
     "vite-plugin-top-level-await": "^1.5.0",
-    "vite-tsconfig-paths": "^4.3.2"
+    "vite-tsconfig-paths": "^4.3.2",
+    "vitest": "^2.1.9"
   }
 }