Ignore unknown capabilities and always assume markdown

[mrmara]

webui ignores unknown capabilities. They are shown but do not have any effect on the UI.

Supported capabilities are now:

• text
• vision
• thinking

Moreover notation text:markdown has been dropped and now all text is assumed to be markdown

[farshidtz]

webui now ignores unknown capabilities and silently do not show them in configs.

Web UI is expected to display all capabilities (text, vision, thinking, tools, etc) and react to known ones accordingly. It should not error out on an unknown capability. For example, when vision is there, it should show an attach button. For thinking, it should show a toggle. audio should just be displayed.

[jpm-canonical]

This change looks good to me, but I think we can do a larger cleanup here. We always assume Markdown. We do not need to specifically document it, nor keep the isMarkdown computed property. What happens if we remove the isMarkdown property, and all code that refers to it, and just keep the markdown code branches?

[jpm-canonical]

LGTM, but please drop changes to package-lock.json

Addressed