Linux image-clipboard detection gives up on `xclip` failure and never tries `wl-paste`

[offbyonebit]

Severity: medium
Type: bug
Location: clipsync/clipboard.py — _read_image_from_system_clipboard() (~line 350)

Problem: The first probe loop tries xclip -t TARGETS then wl-paste --list-types. If xclip is installed but fails (e.g., on a Wayland session without Xwayland), the code returns None immediately instead of continuing to the wl-paste fallback, breaking image detection on hybrid Linux setups.

Suggested fix: Change the return None after a non-zero xclip result to continue, so the loop falls back to wl-paste just like the second image-fetch loop already does.

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_{Filed from a full-source audit of the repo (2026-07-29). Independently confirmed against the source before filing.}