fix(wayland): acquire keyboard focus on layer startup

[devmobasa]

Summary

• request exclusive keyboard interactivity while a main layer surface is acquiring initial focus
• restore normal toolbar policy only after a valid current-surface enter while preserving release precedence
• reject stale enters using the surface identity, committed interactivity cache, and release state
• preserve acquired state across ordinary keyboard teardown and cover lifecycle and policy transitions

Validation

• ./tools/lint-and-test.sh under Rust 1.95
• 10 focused policy, eligibility, and lifecycle tests
• git diff --check

Manual compositor validation was not run because opening the overlay would affect foreground focus.