Add Gitea email configuration and document SMTP authentication troubleshooting

Changes:
- Configure Gitea mailer with Titan Email SMTP settings
- Add SMTP_AUTH = PLAIN for authentication method specification
- Update SMTP password in vault (vault_gitea_smtp_password)

Email Status:
Currently non-functional due to SMTP authentication rejection by Titan Email
servers. Error: 535 5.7.8 authentication failed

Troubleshooting Performed:
- Tested both port 587 (STARTTLS) and 465 (SSL/TLS)
- Verified credentials work in webmail
- Tested AUTH PLAIN and AUTH LOGIN methods
- Removed conflicting TLS settings
- Both authentication methods rejected despite correct credentials

Root Cause:
The issue is NOT a Gitea configuration problem. Titan Email SMTP server
is rejecting all authentication attempts from the VPS (69.62.119.31)
despite credentials being correct and working in webmail.

Possible causes:
- SMTP access may need to be enabled in Hostinger control panel
- VPS IP may require whitelisting
- Account may need additional verification for SMTP access
- Titan Email plan may not include external SMTP access

Documentation:
Created comprehensive troubleshooting guide at:
docs/gitea-email-troubleshooting.md

Files Modified:
- roles/gitea/templates/app.ini.j2 (+1 line: SMTP_AUTH = PLAIN)
- docs/gitea-email-troubleshooting.md (new file, complete troubleshooting log)
- host_vars/arch-vps/vault.yml (updated SMTP password - not committed)

Next Steps:
- Check Hostinger control panel for SMTP/IMAP access toggle
- Test SMTP from different IP to rule out IP blocking
- Contact Hostinger/Titan support for SMTP access verification
- Consider alternative email providers if Titan SMTP unavailable

roles/gitea/templates/app.ini.j2

@@ -87,7 +87,6 @@ OPENID_CONNECT_SCOPES = {{ gitea_oauth2_scopes }}
 REGISTER_EMAIL_CONFIRM = {{ gitea_oauth2_register_email_confirm | lower }}
 
 [mailer]
-# === Email Configuration (Titan Email) ===
 ENABLED = {{ gitea_mailer_enabled | lower }}
 {% if gitea_mailer_enabled %}
 PROTOCOL = {{ gitea_mailer_protocol }}
@@ -98,7 +97,7 @@ USER = {{ gitea_mailer_user }}
 PASSWD = {{ gitea_mailer_password }}
 SUBJECT_PREFIX = {{ gitea_mailer_subject_prefix }}
 SEND_AS_PLAIN_TEXT = false
-ENABLE_HELO = true
+SMTP_AUTH = PLAIN
 {% endif %}
 
 [session]