feat: auto-convert unsupported image formats (AVIF, HEIC) to PNG

[RaviTharuma]

Issue for this PR

Closes#17772
Also addresses #12519 and #10609 (same root cause — unsupported image formats hitting provider APIs)

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

AI provider APIs (Anthropic, OpenAI, Google) only accept PNG, JPEG, GIF, and WebP images. When users reference AVIF, HEIC, TGA, or other unsupported files, the API returns a 400 error like image/avif is not a supported media type.

This adds transparent conversion in File.read() — when an image has an unsupported MIME type (AVIF, HEIC, HEIF, JXL, TIFF, BMP), it converts to PNG before base64-encoding. The conversion uses a 3-tier fallback:

1. sharp (added as optional dependency — fast, cross-platform)
2. sips (always available on macOS)
3. ffmpeg (cross-platform fallback)

If none are available, the original format is sent as-is (same as current behavior — no regression).

Also adds AVIF/HEIC/HEIF entries to the TUI MIME_BADGE map so these formats display the "img" badge.

How did you verify your code works?

• Tested AVIF→PNG conversion with sips on macOS using real AVIF web assets
• Verified standard PNG/JPEG images pass through unchanged (no conversion overhead)
• Confirmed graceful fallback when no converter is available

Screenshots / recordings

N/A — no UI change beyond badge labels.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

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[rekram1-node]

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