Move export app under backend/export

[pashiav]

Fixes #6769

This PR reorganizes the project structure by moving the export app into a new backend/export/ directory under specifyweb/.

Summary of Changes:

• Moved export to specifyweb/backend/export/
• Updated all import paths to reflect the new location
• Updated SPECIFY_APPS in settings.py to include specifyweb.backend.export

This is the 12th PR in a broader backend reorganization. No frontend behavior or functionality was changed.

Notes:

• This PR requires a rebuild for the changes to take effect properly.
• This PR is built on Reorganize report_runner app under backend/report_runner/ #6763.

Checklist

• Self-review the PR after opening it to make sure the changes look good and
  self-explanatory (or properly documented)
• Add relevant issue to release milestone
• Add pr to documentation list
• Add automated tests
• Add a reverse migration if a migration is present in the PR

Testing instructions

DwCA Data Exporting in Specify 7 Documentation

Please cross check the following functionalities with main.

• General testing of Exports (additional gen testing in addition to the ones below)
  Verify that you can:

  • Go to Queries
  • Click the Edit pencil icon on any saved Query
  • Click Export
  • See a JSON file has been downloaded
  
  

  Use a database with DwCA configured (e.g. KU_Fish):

  • Go to User Tools
  • Under Export, click Create DwC Archive
  • Make sure you select the DwCA and metadata from the same collection that you're in
  • Wait to receive a notification "DwCA export completed." then click Download
  • DwCA zip file is downloaded and the content inside of it is the same as on main

8mb.video-Qam-upLvTLun.mp4

[bhumikaguptaa]

• General testing of Exports (additional gen testing in addition to the ones below)
  • See a JSON file has been downloaded
  • DwCA zip file is downloaded and the content inside of it is the same as on main

Looks good and everything is working but there is one error message connected to the following bug report that pops up - #2920

[emenslin]

• General testing of Exports (additional gen testing in addition to the ones below)
  • See a JSON file has been downloaded
  • DwCA zip file is downloaded and the content inside of it is the same as on main

Looks good!

[pashiav]

@bhumikaguptaa Appreciate you pointing that out! It looks like it’s unrelated to this PR - would you mind giving this another quick review?

[lexiclevenger]

• General testing of Exports (additional gen testing in addition to the ones below)
  • See a JSON file has been downloaded
  • DwCA zip file is downloaded and the content inside of it is the same as on main

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Looks good! I didn't run into issues with either type of export.