chore: initialize repository with project docs and tooling

- Add persistent docs: PRD, functional design, architecture, repository structure, development guidelines, milestones

- Add brainstorming notes (docs/ideas/)

- Configure tooling: package.json, tsconfig, eslint, prettier, vitest

- Add opencode configuration (commands, skills, agents)

- Add .gitignore for node_modules, .env, data/, backups/, build outputs

vitest.config.ts

@@ -0,0 +1,29 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: 'node',
+    include: [
+      'src/**/*.{test,spec}.{ts,tsx}',
+      'tests/**/*.{test,spec}.{ts,tsx}',
+    ],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'json', 'html'],
+      exclude: [
+        'node_modules/**',
+        'dist/**',
+        '.steering/**',
+        '**/*.config.{ts,js}',
+        '**/types/**',
+      ],
+      thresholds: {
+        branches: 80,
+        functions: 80,
+        lines: 80,
+        statements: 80,
+      },
+    },
+  },
+});