Render local images in the Kitty TUI

[FelixZhang]

Summary

Adds optional local image rendering to the interactive TUI using Kitty's graphics protocol. Rendering is disabled by default and can be enabled through configuration, environment, or an in-session hotkey.

Changes

• Add kitty-images configuration with LEAF_KITTY_IMAGES override; both default to disabled.
• Add an i / I session toggle with status feedback and help entry.
• Parse ![alt](source) into image blocks only when image rendering is enabled.
• Render local PNG, JPEG, GIF, and WebP images in the Kitty TUI using ratatui-image.
• Decode and encode visible images on a background worker, with cancellation and retry handling.
• Size image blocks from the source image aspect ratio and clamp the reserved height to 12–40 rows.
• Keep disabled mode on the existing upstream Markdown path: only alt text is shown, with no image border or reserved rows.
• Preserve readable fallbacks for missing, oversized, remote, SVG, unsupported, table, and footnote images.
• Leave --inline output unchanged and free of Kitty control sequences.

Notes

• Local paths resolve relative to the Markdown file; stdin paths resolve relative to the current working directory.
• HTTP(S), data: URLs, and SVG files are not downloaded or rendered.
• Images are bounded to 20 MiB, 16,384 pixels per dimension, and 128 MiB decode allocation.

Testing

• cargo fmt --all -- --check
• cargo test (540 tests)
• cargo clippy --all-targets --all-features -- -D warnings
• cargo build --release
• Verified --inline contains no Kitty APC sequences
• Manual Kitty visual verification: see the Kitty Images section in TESTING.md

[RivoLink]

Duplicate of #200

Hi,
As I mentioned in #295, I’m sorry, but I’m not planning to add image preview support to leaf.