docs: update CLAUDE.md and README.md with Mattermost and Netdata

Updated documentation to reflect current infrastructure:

**Added:**
- Mattermost team collaboration platform
  - Team chat, file sharing, integrations
  - Email notifications via IONOS SMTP
  - Incoming webhooks for infrastructure alerts
  - PostgreSQL backend

- Netdata real-time monitoring
  - System and service monitoring
  - PostgreSQL and Docker monitoring
  - Restic backup repository monitoring
  - Email and Mattermost alerts
  - HTTP Basic Auth protection

**Removed:**
- Gotify notification server (replaced by Mattermost)

**Updated:**
- Database initialization: Added mattermost database
- Backup configuration: Added Mattermost volumes
- Environment variables: Added MATTERMOST_WEBHOOK_URL and WATCHTOWER_NOTIFICATION_URL
- Volume management: Added Mattermost, Joplin, and Jellyfin volumes
- Service list in compose include pattern

All documentation now reflects the current state of the infrastructure
with Mattermost as the central notification and collaboration hub.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

README.md

@@ -47,7 +47,7 @@ The **Falcon** is a state-of-the-art containerized starship, powered by Docker's
 | **SEXY** | *Advanced alien encounter database* | [sexy.pivoine.art](https://sexy.pivoine.art) |
 | **AWSM** | *Intergalactic discovery catalog* | [awesome.pivoine.art](https://awesome.pivoine.art) |
 | **TRACK** | *Mission analytics & telemetry* | [umami.pivoine.art](https://umami.pivoine.art) |
-| **GOTIFY** | *Subspace communication relay* | [gotify.pivoine.art](https://gotify.pivoine.art) |
+| **MATTERMOST** | *Crew collaboration & mission control* | [mattermost.pivoine.art](https://mattermost.pivoine.art) |
 | **SCRAPY** | *Web scraping reconnaissance cluster* | [scrapy.pivoine.art](https://scrapy.pivoine.art) |
 | **N8N** | *Automated workflow command center* | [n8n.pivoine.art](https://n8n.pivoine.art) |
 | **STASH** | *Universal file management portal* | [stash.pivoine.art](https://stash.pivoine.art) |
@@ -58,6 +58,7 @@ The **Falcon** is a state-of-the-art containerized starship, powered by Docker's
 | **JELLY** | *Media streaming server* | [jelly.pivoine.art](https://jelly.pivoine.art) |
 | **DROP** | *Peer-to-peer file sharing* | [drop.pivoine.art](https://drop.pivoine.art) |
 | **RESTIC** | *Automated backup vault system* | [restic.pivoine.art](https://restic.pivoine.art) |
+| **NETDATA** | *Real-time ship diagnostics & alerts* | [netdata.pivoine.art](https://netdata.pivoine.art) |
 | **PROXY** | *Shield control dashboard* | [proxy.pivoine.art](https://proxy.pivoine.art) |
 | **VPN** | *Cloaking device network* | [vpn.pivoine.art](https://vpn.pivoine.art) |