feat: add cross-platform focus adapters

[owjs3901]

Summary

• isolate focused-application discovery behind one Rust interface
• add read-only Windows executable and Linux X11 desktop ID/WM_CLASS adapters
• preserve macOS preset/occlusion behavior and keep Wayland on the safe base-four-cell fallback
• align PRD and repository guidance with the cross-platform Tauri scope

Scope

• no registry downloads, caching, matching, or profile-recognition UI in this Wave
• Windows adapter compiled and tested on the implementation host
• macOS and Linux runtime behavior still require verification on those hosts

Verification

• cargo fmt --all --check
• cargo clippy -p hanbeon --all-targets -- -D warnings
• cargo check -p hanbeon --all-targets
• cargo test -p hanbeon — 146 passed
• BUN_RUNTIME_TRANSPILER_CACHE_PATH=0 bun test — 43 passed
• bun run build — desktop and admin builds passed
• independent task reviews and final broad review: no Critical/Important findings

[github-actions]

Changepacks

hanbeon@0.1.0 - package.json

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