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

.prettierrc

@@ -0,0 +1,9 @@
+{
+  "semi": true,
+  "trailingComma": "es5",
+  "singleQuote": true,
+  "printWidth": 80,
+  "tabWidth": 2,
+  "useTabs": false,
+  "arrowParens": "always"
+}