docs: add unified logging system documentation and CI/CD integration (refs #87)

- Update staging workflow to use LOG_LEVEL=DEBUG
- Create docs/LOGGING.md with unified logging documentation
- Delete docs/UX-DEBUGGING.md (replaced by LOGGING.md)
- Update architecture to 9-container (6 app + 3 logging)
- Update CLAUDE.md, README.md, docs/README.md, docs/CLAUDE.md
- Update docs/PLATFORM-SERVICES.md deployment section

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/LOGGING.md

@@ -0,0 +1,118 @@
+# Unified Logging System
+
+MotoVaultPro uses a unified logging system with centralized log aggregation.
+
+## Overview
+
+- **Single Control**: One `LOG_LEVEL` environment variable controls all containers
+- **Correlation IDs**: `requestId` field traces requests across services
+- **Centralized Aggregation**: Grafana + Loki for log querying and visualization
+
+## LOG_LEVEL Values
+
+| Level | Frontend | Backend | PostgreSQL | Redis | Traefik |
+|-------|----------|---------|------------|-------|---------|
+| DEBUG | debug | debug | all queries, 0ms | debug | DEBUG |
+| INFO | info | info | DDL only, 500ms | verbose | INFO |
+| WARN | warn | warn | errors, 1000ms | notice | WARN |
+| ERROR | error | error | errors only | warning | ERROR |
+
+## Environment Defaults
+
+| Environment | LOG_LEVEL | Purpose |
+|-------------|-----------|---------|
+| Development | DEBUG | Full debugging locally |
+| Staging | DEBUG | Full debugging in staging |
+| Production | INFO | Standard production logging |
+
+## Correlation IDs
+
+All logs include a `requestId` field (UUID v4) for tracing requests:
+
+- **Traefik**: Forwards X-Request-Id if present
+- **Backend**: Generates UUID if X-Request-Id missing, includes in all logs
+- **Frontend**: Includes requestId in API call logs
+
+### Example Log Entry
+```json
+{
+  "level": "info",
+  "time": "2024-01-15T10:30:00.000Z",
+  "requestId": "550e8400-e29b-41d4-a716-446655440000",
+  "msg": "Request processed",
+  "method": "GET",
+  "path": "/api/vehicles",
+  "status": 200,
+  "duration": 45
+}
+```
+
+## Grafana Access
+
+- URL: https://logs.motovaultpro.com
+- Default credentials: admin/admin (change on first login)
+
+### Example LogQL Queries
+
+Query by requestId:
+```
+{container="mvp-backend"} |= "550e8400-e29b-41d4"
+```
+
+Query all errors:
+```
+{container=~"mvp-.*"} | json | level="error"
+```
+
+Query slow requests (>500ms):
+```
+{container="mvp-backend"} | json | duration > 500
+```
+
+## Configuration
+
+Logging configuration is generated by `scripts/ci/generate-log-config.sh`:
+
+```bash
+# Generate DEBUG level config
+./scripts/ci/generate-log-config.sh DEBUG
+
+# Generate INFO level config
+./scripts/ci/generate-log-config.sh INFO
+```
+
+This creates `.env.logging` which is sourced by docker-compose.
+
+## Architecture
+
+```
++-----------------------------------------------------------------------+
+|                         CI/CD PIPELINE                                |
+|  LOG_LEVEL --> generate-log-config.sh --> .env.logging                |
++-----------------------------------------------------------------------+
+                                |
+                                v
++-----------------------------------------------------------------------+
+|                       APPLICATION LAYER                               |
+|  Frontend   Backend    OCR      Postgres   Redis    Traefik           |
+|      |         |         |         |         |         |              |
+|      +---------+---------+---------+---------+---------+              |
+|                          |                                            |
+|                Docker Log Driver (json-file, 10m x 3)                 |
++-----------------------------------------------------------------------+
+                           |
+                           v
+              Promtail --> Loki (30-day retention) --> Grafana
+```
+
+## Troubleshooting
+
+### Logs not appearing in Grafana
+
+1. Check Promtail is running: `docker logs mvp-promtail`
+2. Check Loki is healthy: `curl http://localhost:3100/ready`
+3. Verify log rotation is not too aggressive
+
+### Invalid LOG_LEVEL
+
+Both frontend and backend will warn and fall back to 'info' if an invalid LOG_LEVEL is provided.