[BUG] /model picker shows duplicate entry when settings.json model matches a built-in option

Description

When settings.json contains a model key that matches one of the built-in model options, the /model picker shows it twice — once as the built-in entry and again as a separate entry from the config.

Steps to reproduce

1. Set "model": "claude-opus-4-6" in ~/.claude/settings.json
2. Run /model

Observed behavior

The picker shows 4 entries:

1. Default (recommended)   Sonnet 4.6 · Best for everyday tasks
2. Opus                    Opus 4.6 · Most capable for complex work
3. Haiku                   Haiku 4.5 · Fastest for quick answers
4. Opus 4.6 ✓              claude-opus-4-6

Entry #2 and #4 are the same model. The checkmark is on #4 (the settings.json entry), not #2.

Expected behavior

The picker should deduplicate — if the configured model matches a built-in option, just select that built-in option instead of appending a separate entry.

Environment

• Claude Code CLI on Windows 11
• Pro plan (Sonnet shown as "Default")

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