Only allow HTTP adapters for codecompanion result summarisation

[Davidyz]

This is a follow-up of olimorris/codecompanion.nvim#2030, which introduces ACP adapters alongside the regular HTTP adapters. Since the ACP adapters don't share the same interface as the HTTP adapters, it's easier to only allow HTTP adapters to be used here. This is mostly a fail-safe, because the ACP adapters don't use the codecompanion tools OOTB (?).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.66%. Comparing base (84d6d1a) to head (1d12003).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #278   +/-   ##
=======================================
  Coverage   99.66%   99.66%           
=======================================
  Files          24       24           
  Lines        1788     1788           
=======================================
  Hits         1782     1782           
  Misses          6        6           

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