feat: set capabilities for next edit

[jpoly1219]

Description

Closes CON-3283.

Users can now set next_edit as a per-model capability.

Checklist

• I've read the contributing guide
• The relevant docs, if any, have been updated or created
• The relevant tests, if any, have been updated or created

Screen recording or screenshot

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Tests

core/llm/autodetect.vitest.ts

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Summary by cubic

Added support for setting the next_edit capability per model, allowing only specific models to use the next edit feature.

• New Features
  • Models can now declare next_edit capability in their config.
  • Logic checks this capability before enabling next edit in the app and VS Code extension.
  • Added tests to verify correct detection of supported models.

[tingwai]

Looks good, just some quick changes

[RomneyDa]

@tingwai doing prerelease, looks like @jpoly1219 made requested changes, stamping!

requested changes were made.