feat(claude): support image attachments

[owainlewis]

Closes #187

Summary

• send validated images to Claude Code as ordered base64 content blocks through native streaming JSON input
• preserve the existing text-only command and single-result JSON contract
• support new and resumed sessions with typed, base64-safe failures and the shared raw 6 MiB limit
• concurrently write image input and drain Claude output to avoid pipe deadlocks from verbose startup hooks
• enable Telegram images for every supported backend and document the Claude transport

Verification

• cargo test --locked claude
• cargo test --locked gateway
• cargo fmt --all --check
• cargo clippy --locked --all-targets -- -D warnings
• cargo build --locked
• cargo test --locked (456 tests across unit and integration targets)
• deadlock regression: 10,000 startup events before reading a 1 MiB image payload
• independent review: initial I/O finding fixed; final review has no findings

Manual verification

Not run: live Telegram routing requires a configured vision-capable Claude Code provider.

[owainlewis]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

Reviewed commit: d494fe5ef2

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