Add .prettierrc, .prettierignore; update frontend/package.json scripts

- Root .prettierrc sets tabWidth=4 and proseWrap=always
- Root .prettierignore excludes node_modules, build output, lockfiles
- package.json: adds test (vite build), lint, fmt scripts; adds prettier
  as a devDependency; fixes typos in description and keywords

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.prettierignore

@@ -0,0 +1,6 @@
+node_modules/
+frontend/dist/
+frontend/build/
+backend-go/bin/
+*.lock
+Prompts/