feat: add Slite integration

[pranavrajs]

Adds the Slite integration (Others). Search Slite notes, read their content, and ask Slite's AI questions about your knowledge base.

Tools

• Search Notes (search_notes, GET)
• Get Note (get_note, GET)
• List Notes (list_notes, GET)
• List Child Notes (list_child_notes, GET)
• Ask Question (ask_question, GET)

Testing

• The manifest passes the validator ("valid": true).
• Every template was rendered locally with Liquid 5.4.0 against sample responses built from Slite's API docs.
• Not run against the live API. No credentials were available, so tool-tester.rb has not been run with a real key. This needs doing before merge.
• No logo is included.

Review notes

• Slite's docs conflict on auth (bearer in the API reference, x-slite-api-key in the older guide). The manifest uses bearer; switch if a live test returns 401.
• Ask Question can take up to ~50 seconds, but Captain times out at 20.

The root README.md row and .env.example entry for this integration are in a separate PR, so the per-integration PRs do not conflict with each other.

[pranavrajs]

Closing: not widely used in the catalog's target markets (US, India, Europe, Brazil, Argentina).