feat(vscode): implement agent model and variant override dropdowns in VSCode settings

[kilo-code-bot]

Supersedes #10089 by @shssoichiro; the feature commit was cherry-picked with Josh Holmer preserved as the author.
This org-owned branch lets the visual regression workflow update screenshot baselines, which cannot be committed back to the forked PR.

Original PR: #10089

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (9 files)

• .changeset/agent-variant-override.md
• packages/kilo-vscode/tests/unit/config-utils.test.ts
• packages/kilo-vscode/tests/unit/mode-model.test.ts
• packages/kilo-vscode/webview-ui/src/components/settings/ModeEditView.tsx
• packages/kilo-vscode/webview-ui/src/components/settings/mode-model.ts
• packages/kilo-vscode/webview-ui/src/components/shared/ThinkingSelector.tsx
• packages/kilo-vscode/webview-ui/src/stories/settings.stories.tsx
• packages/kilo-vscode/webview-ui/src/stories/StoryProviders.tsx
• packages/kilo-vscode/webview-ui/src/types/messages/agents.ts
• i18n files (16 locales)

Notes:

• modelPatch correctly handles all edge cases: clearing the model clears the variant together, switching to a model that doesn't support the current variant clears it, and keeping the variant when the new model supports it.
• The conditional globalTrigger guard (registering the openVariantPicker listener only when needed) is sound since it's evaluated once at component init and the prop is always passed as a static literal.
• The showVariant sentinel logic (!!cfg().variant won't fire on null) is correct — null is the delete sentinel not a truthy override value.
• Minor: mode-model.test.ts has no test for modelPatch(provider, model, [], null) (switching to a variant-less model when variant was already cleared), but the behavior is correct by inspection.

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_{Reviewed by claude-sonnet-4.6 · 653,551 tokens}

_{Review guidance: REVIEW.md from base branch main}

[shssoichiro]

Unit test failure seems spurious