Improve settings and wizard UX

[yzx9]

• The logic for our current settings and wizard interfaces is nearly identical, but they rely on different types. We should unify these types to keep the implementation consistent and avoid confusing users.
• Filter vision-supported models
• Cleanup model and api keys after switch provider
• Fixed width and height
• Reserve space for error messages to avoid flickering
• Re-detect vision capability when LLM changed
• Openrouter model listing not complete
• Cleanup form when provider changed
• DDG configuration

[00JackLu]

• Vision enabled stills has [Vision not available], mainly because the Filter vision-supported models not includes Pro/moonshotai/Kimi-K2.5.