chore: replace generic emails with GitHub references (#261)

## Summary

- Replace generic `@netresearch.de` email addresses with GitHub-native
references
- Add `support` section to package metadata with Issues/Source URLs
- Use GitHub Security Advisories for vulnerability reporting
- Use GitHub Issues for general support/contact

## Motivation

Generic email addresses in public repositories attract spam and create
maintenance overhead. GitHub provides better mechanisms for each use
case:
- **Security**: Private vulnerability reporting via Security Advisories
- **Support**: Issue tracker with templates and labels
- **Contact**: Discussions for general questions

## Test plan

- [ ] Verify package metadata is valid (composer validate)
- [ ] Verify links in documentation point to correct URLs
- [ ] Verify no functional email addresses were removed (only
metadata/docs)

Author: CybotTM

src/Model/JsonResponse.php

@@ -13,7 +13,7 @@
  *
  * @category   Netresearch
  *
- * @author     Various Artists <info@netresearch.de>
+ * @author     Various Artists
  * @license    http://www.gnu.org/licenses/agpl-3.0.html GNU AGPl 3
  *
  * @see       http://www.netresearch.de
@@ -30,7 +30,7 @@
  *
  * @category   Netresearch
  *
- * @author     Various Artists <info@netresearch.de>
+ * @author     Various Artists
  * @license    http://www.gnu.org/licenses/agpl-3.0.html GNU AGPl 3
  *
  * @see       http://www.netresearch.de

src/Model/Response.php

@@ -13,7 +13,7 @@
  *
  * @category   Netresearch
  *
- * @author     Various Artists <info@netresearch.de>
+ * @author     Various Artists
  * @license    http://www.gnu.org/licenses/agpl-3.0.html GNU AGPl 3
  *
  * @see       http://www.netresearch.de
@@ -28,7 +28,7 @@
  *
  * @category   Netresearch
  *
- * @author     Various Artists <info@netresearch.de>
+ * @author     Various Artists
  * @license    http://www.gnu.org/licenses/agpl-3.0.html GNU AGPl 3
  *
  * @see       http://www.netresearch.de

src/Util/PhpSpreadsheet/LOReadFilter.php

@@ -9,7 +9,7 @@
  *
  * @category   Netresearch
  *
- * @author     Various Artists <info@netresearch.de>
+ * @author     Various Artists
  * @license    http://www.gnu.org/licenses/agpl-3.0.html GNU AGPl 3
  *
  * @see       http://www.netresearch.de