feat(dash): scrollbars on scrolling panels, with click-and-drag

[michaelroy-amd]

What

Panels gave no visual sign when their content overflowed, and there was no way to grab a scrollbar with the mouse.

• Reusable panel::vertical_scrollbar / horizontal_scrollbar helpers: no-op when content fits, otherwise draw a bar and return the shrunk content rect.
• Wired into the job console (vertical + horizontal), the LOGS dock, bench detail, chat transcript, and all seven list managers.
• Click-and-drag: each drawn bar records a per-frame hit-test handle; a click on a track jumps to that position and arms a drag that keeps tracking the pointer until release. The tail-anchored LOGS dock offset is inverted so dragging down goes toward older lines.
• Also clamps the job console's horizontal offset against the widest line.

Excluded on purpose: the list managers' bars are drag-to-jump-selection would be awkward (they're driven by ListState selection), so those show a bar but aren't draggable. Easy follow-on.

Tests

• panel::tests: no-op-when-fits, shrink-on-overflow (V and H).
• app::tests: proportional position mapping, full grab → drag → release cycle, dock inversion.
• Full crate suite green (--test-threads=1), clippy -D warnings clean.

Notes

Part 2 of 3. Stacked on #91 (both touch the draw_job_console signature / call site) — please merge #91 first, then this retargets to main.

[rominf]

LGTM. Shared scrollbar helper (no duplicated math), correct clamping (saturating_sub; div-by-zero guarded by max_pos == 0 / span <= 1 early returns), proportional offset math, no panics. Verified drag-when-bar-disappears, DockLogs tail-anchored inversion, and last-track-cell → max_pos mapping against the included unit tests.

Two minor notes:

1. Horizontal drag clamps to content_w - vbody.width while the keyboard allows one extra column (content_w - 1) — a 1-cell inconsistency in max horizontal offset worth aligning.
2. The manager-list scrollbars (engine/config/runtime/services/update/automations, folder_browser) render but aren't hit-tested (no record_scrollbar) and track selected rather than the scroll offset — looks intentional for this PR's scope, but the mix of grabbable/non-grabbable bars is a UX rough edge worth a note in the description.

Approving.

[volen-silo]

🔴 Automated review · pr-review-watcher · 2162f28

Summary

Adds reusable vertical/horizontal scrollbar helpers and wires them into the job console, LOGS dock, bench detail, chat transcript, and the seven list managers, with click-and-drag hit-testing for the first four. Verdict: Approve — this is a clean, well-tested change. Verified: cargo build/test(571 pass, --test-threads=1)/clippy -D warnings/fmt --check all clean; confirmed the drag position math (position_at proportional map + DockLogs tail inversion), the per-frame RefCell registry lifecycle (cleared+rebuilt every draw/draw_focused, mutually exclusive, no stale handles or borrow conflicts), and that the two initially-suspected "blocking" issues de-verify to pre-existing behavior / non-crashing visual imprecision. Blocking: 0 · Non-blocking: 4.

🚫 Blocking (must fix before merge)

None.

Non-blocking

• ui/tabs/chat.rs:240, ui/tabs/bench.rs:458 — scrollbar is told content_len = lines.len() (pre-wrap) while the Paragraph renders with .wrap(Wrap{trim:false}), so when lines wrap the thumb under-reports extent (may not appear on real overflow) and chat drag maps to an imprecise offset; either measure wrapped rows for content_len or drop .wrap(). (Inherits a pre-existing scroll imprecision, now made visible.)
• 7 list managers (e.g. ui/config_manager.rs:272) — these bars are draw-only (no record_scrollbar/ScrollTarget), so the PR summary bullet reading as "click-and-drag" for them is slightly ambiguous vs the body's noted exclusion; worth tightening the wording.
• 7 list managers — pass selected (selection index) as the bar position, so the thumb tracks the cursor rather than the viewport top and sits mid-track when it should be near an edge; cosmetic only since these bars aren't hit-tested.
• Test gaps: no unit test for the ScrollbarHandle::new no-op branch (drawn == area → None, guards against a phantom clickable region), and no drag/release test for the horizontal ConsoleH grab path (only vertical targets are exercised end-to-end).