Scroll TUI widgets as a single panel

[edwin-zvs]

Summary

• Render visible TUI widgets into one stacked popover/panel instead of separate clipped cards
• Add a per-session widget-panel scroll offset and a single scrollbar for the stacked widget panel
• Route mouse-wheel scrolling over the widget panel to the widget panel rather than terminal scrollback
• Route Up/Down/PageUp/PageDown to widget-panel scrolling while a widget panel is focused
• Translate widget action/close hitboxes by the panel scroll offset so clicks match visible content

Validation

• cargo build -p agentd-cli
• cargo test -p agentd-cli dynamic_ui -- --nocapture (no matching tests; command completed successfully)
• git diff --check

Notes

• This PR only touches crates/cli TUI code; relevant binary is agent.
• No recording attached: behavior is scroll/input plumbing rather than a static visual change, and local build validation covers compilation.

[edwin-zvs]

Follow-up polish:

• Added a single outer border around the stacked TUI widget panel.
• Moved widget content/scrollbar into the bordered inner area so hitboxes and scrollbar stay aligned.
• Changed widget temporary/autohide extension from 10s to 15s via DYNAMIC_UI_AUTOHIDE_SECS.

Validation:

• cargo fmt on touched TUI files
• cargo build -p agentd-cli
• git diff --check

[edwin-zvs]

Focus polish for the shared widget panel:

• Focused widget title row now uses a reversed/accent highlight across the row.
• Focused widget body rows get a left accent marker so it is clear which section owns keyboard shortcuts/input.
• Non-focused widget sections remain visually quieter inside the shared bordered panel.

Validation:

• cargo fmt on touched TUI file
• cargo build -p agentd-cli
• git diff --check

[edwin-zvs]

Removed the outer widget panel title; the shared panel keeps its single border and per-widget titles/focus affordance.

[edwin-zvs]

Updated the TUI widget panel polish per feedback:\n\n- Removed the dotted/thick left body focus marker.\n- Focused widget sections now use a 1-cell bright green left/right edge.\n- Removed the scrollbar track line; only the thumb remains.\n- Shifted the per-widget hide button left so it no longer overlaps the scrollbar gutter.\n\nValidation: cargo build -p agentd-cli, git diff --check.

[edwin-zvs]

Follow-up polish pushed:\n\n- Removed the per-widget left/right border styling entirely; focus is now title-row highlight only.\n- Kept the scrollbar track removed.\n- Fixed the close-button hitbox so clicks line up with the rendered [-] at the right end of the title row.\n\nValidation: cargo build -p agentd-cli, git diff --check.