feat: support uncommitted changes contextualization and output mode

[google-labs-jules]

• Adds a new "Select output mode" prompt (single vs multiple)
• Adds "Uncommitted Changes" to directory selection prompt.
• Extracts tracked modifications with git diff and untracked files with git ls-files
• Aggregates the single content or dumps everything sequentially based on selected output mode.

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*PR created automatically by Jules for task 10576117334335527033

[google-labs-jules]

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