feat(monitoring): add Redis exporter + Sentry docs to deployment guide

- Add redis-exporter container to docker-compose (oliver006/redis_exporter, 32MB)
- Add Redis scrape target to Prometheus config
- Add 4 Redis alert rules: RedisDown, HighMemory, HighConnections, RejectedConnections
- Document Step 19b (Sentry Error Tracking) in Hetzner deployment guide
- Document Step 19c (Redis Monitoring) in Hetzner deployment guide
- Update resource budget and port reference tables

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/development/synology-github-repo.md

@@ -11,11 +11,11 @@ Git is an open-source, distributed version control system that helps you manage
 ## 🛠️ Create a Git Repository
 
 1. **Sign in to DSM** using an account with administrative privileges.
-2. Go to:  
-   **Control Panel > Terminal & SNMP > Terminal**  
+2. Go to:
+   **Control Panel > Terminal & SNMP > Terminal**
    → Enable **SSH service**.
-3. Go to:  
-   **Control Panel > Shared Folder**  
+3. Go to:
+   **Control Panel > Shared Folder**
    → Create a shared folder for Git repositories.
 4. On your computer, access Synology NAS via SSH:
 
@@ -63,7 +63,7 @@ Adding new repository on NAS DS223J
     > chown -R git-boulaht1:users my-repo.git
     > cd my-repo.git/
   ```
-  
+
 ---
 
 ### ✅ **Steps to Push Local Git Repo to Synology NAS**
@@ -110,9 +110,9 @@ and then Permission and then tick boxes apply to sub folder and files
 (git-boulaht1 should be read write on the folder)
 
 
-> ⚠️ **Note:**  
-> Do **not** perform the above commands with root permissions.  
-> Git Server no longer supports `git-shell` commands due to security concerns.  
+> ⚠️ **Note:**
+> Do **not** perform the above commands with root permissions.
+> Git Server no longer supports `git-shell` commands due to security concerns.
 > For `git-shell` access, consider using container-based Git services.
 
 ---
@@ -149,4 +149,4 @@ and then Permission and then tick boxes apply to sub folder and files
    cd /volume1/mysharefolder/myrepo1
    ```
 
----
+---