Avoid panic on X11 IME unfocus failure

[warp-agent-staging]

Summary

Prevent EventProcessor::xinput2_unfocused from panicking when Xlib reports an error while unfocusing an input context. The error is logged and the existing focus-loss cleanup continues; successful unfocus behavior is unchanged.

Addresses fatal issue ID 7723139261.

• Sentry issue: https://warpdotdev.sentry.io/issues/WARP-CLIENT-BETA-STABLE-8AQ7
• Sentry event: https://sentry.io/organizations/warpdotdev/issues/7723139261/events/cb2ed86e499940f9b60d1bc4b803b130/

Verification

• cargo +nightly fmt --manifest-path /workspace/winit/Cargo.toml --all -- --check
• cargo check --manifest-path /workspace/winit/Cargo.toml --no-default-features --features x11

A focused regression test would require introducing an XIM/X11 test seam into the event processor, so this patch does not add one.

• Tested on all platforms changed (Linux/X11 compile check)
• Added an entry to the changelog module; this contained fatal-handling correction does not change the public API
• Updated documentation; there is no user-facing API or platform behavior to document
• Created or updated an example program; no example is applicable to this error branch

[warp-agent-staging]

This PR was generated with Warp.

Comment @warp-staging-factory on this PR to send it follow-up work.