centralize guides and rails under mosaic with runtime compatibility links

guides/frontend.md

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+# Frontend Development Guide
+
+## Before Starting
+1. Check assigned issue in git repo: `~/.mosaic/rails/git/issue-list.sh -a @me`
+2. Create scratchpad: `docs/scratchpads/{issue-number}-{short-name}.md`
+3. Review existing components and patterns in the codebase
+
+## Development Standards
+
+### Framework Conventions
+- Follow project's existing framework patterns (React, Vue, Svelte, etc.)
+- Use existing component library/design system if present
+- Maintain consistent file structure with existing code
+
+### Styling
+- Use project's established styling approach (CSS modules, Tailwind, styled-components, etc.)
+- Follow existing naming conventions for CSS classes
+- Ensure responsive design unless explicitly single-platform
+
+### State Management
+- Use project's existing state management solution
+- Keep component state local when possible
+- Document any new global state additions
+
+### Accessibility
+- Include proper ARIA labels
+- Ensure keyboard navigation works
+- Test with screen reader considerations
+- Maintain color contrast ratios (WCAG 2.1 AA minimum)
+
+## Testing Requirements (TDD)
+1. Write tests BEFORE implementation
+2. Minimum 85% coverage
+3. Test categories:
+   - Unit tests for utility functions
+   - Component tests for UI behavior
+   - Integration tests for user flows
+
+### Test Patterns
+```javascript
+// Component test example structure
+describe('ComponentName', () => {
+  it('renders without crashing', () => {});
+  it('handles user interaction correctly', () => {});
+  it('displays error states appropriately', () => {});
+  it('is accessible', () => {});
+});
+```
+
+## Code Style
+- Follow Google JavaScript/TypeScript Style Guide
+- **TypeScript: Follow `~/.mosaic/guides/typescript.md` — MANDATORY**
+- Use ESLint/Prettier configuration from project
+- Prefer functional components over class components (React)
+- TypeScript strict mode is REQUIRED, not optional
+
+### TypeScript Quick Rules (see typescript.md for full guide)
+- **NO `any`** — define explicit types always
+- **NO lazy `unknown`** — only for error catches and external data with validation
+- **Explicit return types** on all exported functions
+- **Explicit parameter types** always
+- **Interface for props** — never inline object types
+- **Event handlers** — use proper React event types
+
+## Commit Format
+```
+feat(#123): Add user profile component
+
+- Implement avatar display
+- Add edit mode toggle
+- Include form validation
+
+Refs #123
+```
+
+## Before Completing
+1. Run full test suite
+2. Verify build succeeds
+3. Update scratchpad with completion notes
+4. Reference issue in commit: `Fixes #N` or `Refs #N`