Implement Phase 9: Prometheus Metrics (v0.9.0)

- Add Prometheus metrics integration via wp-prometheus hooks
- Create Grafana dashboard JSON with 24 panels
- Add metrics settings tab with enable/disable toggle
- Expose inventory, booking, occupancy, revenue, and guest metrics

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

PLAN.md

@@ -180,15 +180,23 @@ This document outlines the implementation plan for the WP BnB Management plugin.
 - [x] Guest statistics
 - [x] Export functionality (CSV, PDF)
 
-## Phase 9: Prometheus Metrics (v0.9.0)
+## Phase 9: Prometheus Metrics (v0.9.0) - Complete
 
-- [ ] Meanigful Metrics for this Plugin, see <https://src.bundespruefstelle.ch/magdev/wp-prometheus/raw/branch/main/README.md> for implementation details
-- [ ] Example Grafana-Dashboard, see <https://src.bundespruefstelle.ch/magdev/wp-prometheus/raw/branch/main/README.md> for implementation details
-- [ ] Update settings page to enable/disable metrics
+- [x] Meaningful Metrics for this Plugin:
+  - Inventory: buildings, rooms by status, services by status
+  - Bookings: by status, check-ins/check-outs today, upcoming, avg duration
+  - Guests: total, by status, repeat guests, new this month
+  - Occupancy: current rate, monthly rate, occupied rooms, bed capacity
+  - Revenue: this month, YTD, average booking value, services revenue
+- [x] Example Grafana Dashboard:
+  - Pre-configured dashboard JSON at `assets/grafana/wp-bnb-dashboard.json`
+  - Automatic registration with wp-prometheus
+  - 24 panels with gauges, pie charts, and stat displays
+- [x] Update settings page to enable/disable metrics
 
 ## Phase 10: Security Audit (v0.10.0)
 
-- [ ] Check for Wordpress best-practises
+- [ ] Check for Wordpress best-practices
 - [ ] Review the code for OWASP Top 10, including XSS, XSRF, SQLi and other critical threads
 
 ## Future Considerations (v1.0.0+)
@@ -308,6 +316,6 @@ The plugin will provide extensive hooks for customization:
 | 0.6.0   | Frontend           | Complete |
 | 0.7.0   | CF7 Integration    | Complete |
 | 0.8.0   | Dashboard          | Complete |
-| 0.9.0   | Prometheus Metrics | TBD      |
+| 0.9.0   | Prometheus Metrics | Complete |
 | 0.10.0  | Security Audit     | TBD      |
 | 1.0.0   | Stable Release     | TBD      |