fix(ci): resolve Linux AppImage purge path

[BOTOOM]

Summary

Fix the Linux release workflow after the 1.4.0 release failed during the AppImage purge step.

Root cause

The workflow built the Linux bundle successfully, but the post-build purge step looked for the AppImage in a hardcoded path:

• src-tauri/target/release/bundle/appimage/

When the release workflow builds with an explicit Rust target (--target x86_64-unknown-linux-gnu), Tauri writes the bundle under the target-specific directory, so the purge step could not find the generated AppImage and failed before uploading Linux assets.

Changes

• search for the AppImage under src-tauri/target using a target-agnostic path pattern
• derive the AppImage directory dynamically from the discovered file path
• keep the rest of the purge/repack flow unchanged

Validation

• local YAML validation passed with no editor errors
• manual release rebuild dispatched for cliprithm-v1.4.0 using this workflow fix