docs: comprehensive documentation overhaul

Add complete documentation structure:
- Frontend architecture documentation
- Database schema documentation
- Deployment guides (Docker, Traefik, Authentik, Environment)
- Development guides (Setup, Testing, Contributing, Quality Gates)
- Deployment architecture documentation
- Updated docs README with complete navigation

All new features and APIs are now documented.
Quality gates: docs only, no code changes

docs/templates/feature-doc.md

@@ -0,0 +1,65 @@
+# Feature Documentation Template
+
+Use this template when documenting a new feature.
+
+## Feature Name
+
+## Overview
+
+Provide a 1-2 sentence description of what this feature does and why it exists.
+
+## How to Use
+
+### Prerequisites
+
+List any prerequisites (e.g., must be logged in, must have project created).
+
+### Step-by-Step Guide
+
+1. **Step 1**: Description of first step
+   - Details
+   - Screenshots if applicable
+
+2. **Step 2**: Description of second step
+   - Details
+
+3. **Step 3**: Description of third step
+   - Details
+
+## Screenshots
+
+Include screenshots or diagrams if they help understanding.
+
+## API Reference
+
+List related API endpoints with links to API docs.
+
+### Endpoints
+
+- `METHOD /endpoint/path` - Brief description
+- `METHOD /endpoint/path` - Brief description
+
+## Configuration
+
+List any relevant configuration options (environment variables, settings).
+
+| Option | Description | Default |
+|--------|-------------|---------|
+| `VAR_NAME` | What this controls | `default_value` |
+
+## Troubleshooting
+
+### Common Issues
+
+**Issue**: Description of problem
+**Solution**: How to fix it
+
+## Related Features
+
+- [Feature Name](link.md) - How this relates
+- [Feature Name](link.md) - How this relates
+
+## See Also
+
+- [API Documentation](../api/feature.md)
+- [Architecture Documentation](../architecture/feature.md)