fix(linux): adapt paste chord to focused app

[filipeforattini]

Summary

• select Ctrl+Shift+V automatically for a detected terminal when zellij direct delivery is unavailable
• retain Ctrl+V for graphical apps and the configured fallback when focus is unknown
• emit modifiers and V in separate evdev frames to prevent Mutter/Wayland from producing a literal v
• show the selected fallback chord in dit doctor and document the auto behavior

Root cause

Auto delivery only changed behavior for a reachable zellij target. Every other route used one global paste chord, so Alacritty without a selected zellij session received Ctrl+V by default. The chord was also emitted with modifier-down and V-down in one SYN_REPORT, allowing a compositor race.

Validation

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo test --release --no-fail-fast (92 passed, 1 ignored zellij e2e)

Fixes #43

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