Update user docs for Central v2026.2

[matthew-white]

• Upgrade instructions
• Merge Web Forms docs PRs before release
• Entity filtering
  • @sadiqkhoja has pointed out that it will not be possible to use Entity labels in filters for now

[ktuite]

Additional entity filtering docs ideas:

• Reiterate that you can only filter on the non-system properties of entity lists and users (can't use label, uuid, creator, etc)
• Filtering is based on equality only
• Rules can be combined with OR (see some example scenarios)
• You might need to change your data to add a filter property, and at this time, bulk edits can only be done via the API.
  • share a snippet of pyodk code that could add a property, fetch all entities, and then populate the new property, maybe by parsing a field out of a label?
  • share snippet of code showing how to update app users or public links
  • share snipped to check that a specific user is seeing the correct set of entities