Allow image generation requests to omit prompts for models that only
accept image input, and validate required inputs from model metadata
instead of enforcing a text prompt for every request.
Treat authless search providers as executable with built-in defaults so
SearXNG can run without stored credentials, including during provider
auto-selection.
Also align runtime support with Node.js 24 LTS, harden thinking tag
compression and proxy wildcard matching, and update tests for the new
route and runtime behavior.
