Refine paraphrase prompt; forward media modalities and support JSON mode

[hemanth-asirvatham]

Motivation

• Improve paraphrase prompt clarity and fidelity to instructions while removing example blocks that confused guidance.
• Support multimodal paraphrasing by forwarding image/audio/pdf attachments and clarifying behavior per modality.
• Ensure callers can request JSON-only outputs when json_mode is enabled and surface modality/search settings through the API.

Description

• Tighten and rework src/gabriel/prompts/paraphrase_prompt.jinja2 to remove examples, emphasize instruction fidelity, add concise modality guidance, and conditionally require JSON-only output when json_mode is set, with the final output wording changed to the requested phrasing.
• Pass json_mode into prompt rendering and propagate modality/search options from the API by updating src/gabriel/tasks/paraphrase.py to forward prompt_images, prompt_audio, and prompt_pdfs to the underlying helper, call warn_if_modality_mismatch, and use load_image_inputs/load_audio_inputs/load_pdf_inputs when appropriate.
• Expose modality and search_context_size on the paraphrase API in src/gabriel/api.py and wire defaults so web_search and search_context_size behave sensibly when modality == "web".
• Update recursive generation to accept original values for media forwarding and pass search_context_size into get_all_responses.
• Update tests in tests/test_basic.py to add test_paraphrase_modalities_forward_media and adapt existing paraphrase tests to the new signatures and behavior.

Testing

• Added unit test test_paraphrase_modalities_forward_media and updated existing paraphrase tests in tests/test_basic.py to reflect the new API and media-forwarding behavior.
• No automated test suite was executed as part of this rollout (prompt/template and code changes were prepared and committed but not run under pytest).

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Codex Task

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