Dismiss Help before underlying input

[edwin-zvs]

Summary

• make the Help dialog consume keyboard input before focused Program/minibuffer/session routing
• dismiss Help on mouse clicks before underlying hit-testing or child PTY forwarding
• swallow the matching button-up so the dismissing click cannot activate a covered control
• add regressions for focused Program keys and complete click dismissal

Tests

• cargo test -p agentd-cli help_modal_ -- --nocapture
• cargo test -p agentd-cli (840 behavioral tests passed; known timing-sensitive PTY benchmark failed once, then passed in isolation)
• cargo test -p agentd-cli pty_render::tests::many_small_events_stay_fast_as_history_grows -- --exact --nocapture
• cargo test -p agentd-e2e
• cargo build

Visuals

Not recorded: this fixes input routing for the existing Help dialog without changing its appearance.