feat(web): add duplicate action to the T3 Code default theme

[UtkarshUsername]

What Changed

The default T3 Code theme was the only theme without the option to copy, so customizing from the built-in look required Create theme plus a rename. Duplicate now opens the editor seeded from the default palette, named "T3 Code copy", matching the other built-in cards.

Why

The T3 Code card was the only theme card without the copy icon, even though it ships with the app like Grove, Ocean, Ember, Iris, and T3 Chat. The default look isn't backed by a theme definition, so a duplicate had nothing to seed from, but the editor already starts new themes from the standard palette, which is that exact look. So wiring the copy icon there was a one-line-shaped change that made the library uniform. Saving the duplicate creates an installed custom theme and activates it, same as duplicating any other card.

UI Changes

Before:
It was not possible to duplicate the default theme.

After:
It is possible to duplicate the default theme.

default.theme.mp4

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

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Note

Low Risk
Small Theme Settings UI change reusing the existing theme editor flow; no auth, persistence, or security impact.

Overview
Standard built-in theme cards (including T3 Code) now show the same Duplicate control as maintainer and custom themes.

Duplicating opens the theme editor as a new theme (editingThemeId: null) with the standard palette (seedThemeId: null) and a prefilled name like T3 Code copy, so users can fork the default look without using Create theme and renaming manually.

^{Reviewed by Cursor Bugbot for commit 139446a. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add duplicate action to standard theme cards in the T3 Code default theme

Adds an onDuplicate handler to ThemeLibraryCard instances in ThemeSettings.tsx for standard themes. Clicking duplicate opens the theme editor with a pre-populated name in the format '<theme> copy', creating a new custom theme based on the selected standard theme.

^{Macroscope summarized 139446a.}

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[macroscopeapp]

Approvability

Verdict: Approved 270e0ae

This adds a duplicate action for standard theme cards, following the identical pattern already used for maintainer themes. Simple, self-contained UI enhancement with no runtime behavior concerns.

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