feat(tools): add send_image tool for channel image delivery

[penso]

Summary

• Adds a send_image tool that lets the LLM agent send local image files (PNG, JPEG, GIF, WebP) to the current conversation's channel (e.g. Telegram)
• Threads an optional caption parameter through to send_screenshot_to_channels
• Fixes hardcoded image/png MIME type — now parses the actual MIME from the data URI, supporting all image formats

Validation

Completed

• cargo check compiles
• Unit tests cover: MIME lookup, missing/invalid params, unsupported extensions, directory rejection, oversized files, valid encoding with and without caption

Remaining

• just release-preflight
• cargo test
• Manual QA: send an image via Telegram channel and verify it arrives with correct format and caption

Manual QA

1. Start gateway with a Telegram channel configured
2. Ask the agent to send an image file (e.g. a chart or screenshot)
3. Verify the image arrives in Telegram with correct format
4. Verify caption appears when provided

[codspeed-hq]

Merging this PR will improve performance by 52.06%

⚡ 1 improved benchmark
✅ 38 untouched benchmarks
⏩ 5 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	env_substitution	18.4 µs	12.1 µs	+52.06%

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_{Comparing maximilize/feat/send-image-tool (4a87448) with main (58b3148)}

Footnotes

1. 5 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

❌ Patch coverage is 0% with 23 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
crates/chat/src/lib.rs	0.00%	22 Missing ⚠️
crates/gateway/src/server.rs	0.00%	1 Missing ⚠️

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