fix(cua-driver): prevent Linux uinput pointer panics

[f-trycua]

Summary

• bound Linux uinput pointer names to evdev 0.12's 78-byte ceiling, preserving the generated process/nonce suffix
• sanitize control characters and truncate multibyte UTF-8 only at character boundaries
• contain dependency panics and device-construction errors inside the blocking worker
• return {"code":"uinput_unavailable"} instead of unwinding the worker or silently claiming fallback success
• keep later daemon input work usable after a contained construction panic
• exercise the regression against a real /dev/uinput device on the hosted Linux runner

Root cause

evdev 0.12 asserts during VirtualDevice::build when the supplied name exceeds its stricter limit. The name included a caller-controlled session/cursor identifier, so an overlong identifier unwound the Tokio blocking worker before the existing fallback could run. Device creation errors were otherwise swallowed by the XSendEvent fallback, which could report success despite the real-input route being unavailable.

Validation

• cargo fmt --package platform-linux -- --check
• cargo test --locked -p platform-linux (16 host-runnable tests passed on macOS)
• exact-SHA Linux unit run: passed at d9abbf641962a2e667925892cca3bded70b78ca8
• exact-SHA Linux interactive run: source resolution, capture/desktop scope, Electron/Tauri, GTK3 native harness, install smoke, and matrix summary all passed

The real-uinput CI step loads the hosted runner's uinput module, grants access to the ephemeral device, and builds a pointer from an overlong multibyte name through the production function.

Provenance

Salvaged from #2736's original bounded-name implementation; its source commit remains preserved through cherry-pick -x. Reported and diagnosed by @marvinbaudach in #2715.

Fixes #2715.