♻️ refactor(cd): hardcode non-sensitive config in staging workflow

Reduced GitHub Secrets requirements from 21 to 12 by hardcoding
non-sensitive configuration values directly in the workflow file.

Changes:
- Hardcoded: DB/Redis host/port, STAGING_HOST, STAGING_USER, MANA_SERVICE_URL
- Keep as secrets: passwords, API keys, JWT keys, SSH private key
- Updated generate-staging-secrets.sh to reflect reduced secret list
- Added get-ssh-key.sh helper script for SSH key extraction

Benefits:
- Fewer secrets to manage in GitHub
- Configuration visible in code review
- Easier to update non-sensitive values (no UI navigation)
- Better separation of config vs secrets

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

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

scripts/get-ssh-key.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Get SSH Private Key Content for GitHub Secret
+
+echo "================================================"
+echo "  SSH PRIVATE KEY FOR STAGING_SSH_KEY"
+echo "================================================"
+echo ""
+echo "Copy the ENTIRE output below (including BEGIN and END lines):"
+echo ""
+echo "================================================"
+
+cat ~/.ssh/hetzner_deploy_key
+
+echo "================================================"
+echo ""
+echo "This is the value for: STAGING_SSH_KEY"
+echo ""