Round 4 improvements: automated config, relative paths, simplified deployment

- Automate Traefik email substitution in deploy script
- Auto-generate Authelia admin password (saved to ADMIN_PASSWORD.txt)
- Standardize all volume paths to use relative paths (./service/config)
- Switch Traefik to HTTP challenge by default (DNS challenge optional)
- Update documentation with improved setup instructions
- Enhance troubleshooting guide
- Update AGENT_INSTRUCTIONS with new conventions
- Simplify .env.example with clearer guidance

These changes reduce manual configuration steps and improve deployment reliability.

.env.example

@@ -37,12 +37,17 @@ ADMIN_EMAIL=your-email@example.com  # Used for admin user account
 # ====================================
 # AUTHELIA SSO CONFIGURATION
 # ====================================
-# These secrets are AUTO-GENERATED by setup-homelab.sh
-# DO NOT manually set these - the setup script will create them!
+# Generate these secrets with: openssl rand -hex 64
+# The deploy script will use these to configure Authelia
 
-AUTHELIA_JWT_SECRET=will-be-auto-generated-by-setup-script
-AUTHELIA_SESSION_SECRET=will-be-auto-generated-by-setup-script
-AUTHELIA_STORAGE_ENCRYPTION_KEY=will-be-auto-generated-by-setup-script
+AUTHELIA_JWT_SECRET=generate-with-openssl-rand-hex-64
+AUTHELIA_SESSION_SECRET=generate-with-openssl-rand-hex-64
+AUTHELIA_STORAGE_ENCRYPTION_KEY=generate-with-openssl-rand-hex-64
+
+# Authelia Admin Password (OPTIONAL)
+# If not provided, deploy script will generate a random password
+# and save it to /opt/stacks/core/authelia/ADMIN_PASSWORD.txt
+# AUTHELIA_ADMIN_PASSWORD=your-secure-password-here
 
 # SMTP for Authelia Notifications (OPTIONAL)
 # If not configured, notifications are saved to file instead