Bugfix: Send support and notification emails to the new DocApply mailboxes

[az108]

Checklist

General

• I tested all changes and their related features with all corresponding user types.
• Language: I followed the guidelines for inclusive, diversity-sensitive, and appreciative language.
• I chose a title conforming to the naming conventions for pull requests.

Server

• I strictly followed the server coding and design guidelines.

Client

• I strictly followed the client coding and design guidelines.

Motivation and Context

With the rename from TUMApply to DocApply, the AET mailboxes were renamed as well. The new addresses are docapply.aet@xcit.tum.de and support-docapply.aet@xcit.tum.de.

The rename PR (#2627) rewrote the addresses mechanically along with the rest of the tum-apply → doc-apply replacements, which produced doc-apply.aet@xcit.tum.de and support-doc-apply.aet@xcit.tum.de. Those hyphenated addresses are not real mailboxes, so on main today:

• outgoing notification mails default to a sender address that does not exist,
• the support address shown to users on the About Us page, the Privacy page, and the nginx maintenance page is a dead address,
• the fallback support address used in research group invitation mails is a dead address.

Description

Replaced the hyphenated placeholder with the actual mailbox names. No behaviour, structure, or configuration keys changed — only the default address values and the user-facing text.

Server:

• application.yml: default of aet.email.from (AET_EMAIL_FROM) is now docapply.aet@xcit.tum.de.
• ResearchGroupService: @Value fallback for aet.contact-email is now docapply.aet@xcit.tum.de.
• nginx/maintenance.html: support link and label now point to support-docapply.aet@xcit.tum.de.

Client:

• i18n/en/about-us.json, i18n/de/about-us.json: support mailbox address.
• i18n/en/privacy.json, i18n/de/privacy.json: contact address in the data rights paragraph.

The deployed environments set AET_EMAIL_FROM and aet.contact-email explicitly, so this only corrects the checked-in defaults — but those defaults are what local and test runs fall back to.

Steps for Testing

Prerequisites:

1. Log in to DocApply

Checks:

1. Open About Us and confirm the support mailbox reads support-docapply.aet@xcit.tum.de and the mailto: link opens the same address. Switch the language to German and confirm the same.
2. Open Privacy and confirm the contact address in the "Rights to rectification, erasure, and restriction" section reads support-docapply.aet@xcit.tum.de, in both English and German.
3. Open src/main/resources/config/nginx/maintenance.html in a browser and confirm the support link points to support-docapply.aet@xcit.tum.de.
4. With no AET_EMAIL_FROM set, trigger any outgoing mail (e.g. a research group invitation) and confirm the sender is docapply.aet@xcit.tum.de.
5. Confirm no hyphenated address remains: git grep -n "doc-apply\.aet@" returns nothing.

Review Progress

Code Review

• Code Review 1

Manual Tests

• Test 1

[codacy-production]

Up to standards ✅

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[Cathy0123456789]

Code LGTM and tested locally except for outgoing emails since not possible locally, everything works 👍🏼