feat: config files, settings screen, hardware check

- Add config.py with multi-source config (YAML, .env, env vars)
- Add .env.example and config.yaml.example
- Add settings API endpoints (GET/POST /api/v1/settings)
- Add status endpoint (GET /api/v1/status) with hardware subsystem check
- Add settings screen to web client (protected by API token)
- Add localization strings for settings UI
- Add tests for config module and new endpoints
- Update README with config documentation

server/.env.example

@@ -0,0 +1,13 @@
+# PaperDash Configuration
+# Copy this file to .env and fill in your values
+
+# Dashboard PIN (4-digit code for the E-Ink client)
+DASHBOARD_PIN=1234
+
+# API Token (Bearer token for external scripts)
+API_TOKEN=your-secret-token-here
+
+# Server settings
+HOST=0.0.0.0
+PORT=8921
+LOG_LEVEL=INFO