Slack community migration changes

[gabriel-bolbotina]

• Updated the links to product updates in the gallery app
• Removed slack icon and changed community link in README
• Updated the link in input help

[Withalion]

Note for testers: the changelog page in settings should load correctly

[IvaKuklica]

Update for this comment:
While reviewing the Changelog screen, I noticed a few pre-existing issues These are not related to this PR — they already existed in the previous version. I've logged them separately in a new bug report so they're tracked and addressed independently of this change.
Link to the new bug report:----> #4651

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Warning

Testing note:

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• Issue 1. In the in-app Changelog screen, under "Webmaps: Custom background maps," the "Read more in the docs" link incorrectly redirects the user to community.merginmaps.com instead of the relevant documentation page on merginmaps.com.
  The issue applies to all links in the Changelog that are intended to point to a destination other than the community page

• Steps to reproduce:

1. Open the Changelog screen in the app.
2. Locate the "Webmaps: Custom background maps" note (28 July).
3. Tap the "Read more in the docs" link.

• Expected result:
  Tapping "Read more in the docs" should open the documentation page on merginmaps.com

• Actual result:
  The link redirects to the community page (community.merginmaps.com) instead — the same destination as tapping the note title, even though the two links imply different destinations.

Screenrecord:

ScreenRecording_08-12-2026.10-02-15_1.mp4

• Issue 2. There's an unusually large blank space below the note under one of the flagged sections — more whitespace than the spacing used elsewhere in the changelog.
  Screenshot:

• Issue 3. There's an empty bullet point with no text between the 'Sorting' and 'Filtering for multiple selection' items — a rendering glitch leaving a dangling bullet marker.
  Screenshot: