feat: add settings editor mouse input

[mm65x]

Summary

• add pointer hit-testing for visible settings rows and content scrolling
• activate toggles, enum cycling, and edit fields with left clicks
• support mouse-driven review, save confirmation, discard, and close actions

Verification

• cargo fmt -- --check
• cargo test
• cargo clippy -- -W clippy::pedantic -A clippy::module_name_repetitions
• cargo build --release

Fixes #39

[mm65x]

Review

No blocking findings.

Behavior

• Settings mouse events are routed before dashboard handling, so overlay input cannot leak into the dashboard.
• Visible rows use the same popup, content, and scroll geometry as rendering; section headers and outside clicks remain inert.
• Left clicks reuse the existing activation path for toggles, enum cycling, and text/numeric edit mode.
• Wheel events navigate and clamp at the first and last setting.
• Footer hit targets cover review, confirmation, cancellation, discard, and close flows.
• In-progress text edits are isolated from mouse navigation until Enter applies or Escape cancels them.

Verification

• Local format, all tests, clippy, release build, and diff checks pass.
• GitHub Format, Clippy, Linux, macOS, and Windows checks all pass.
• The focused tests cover visible rows, headers, scroll offsets, footer actions, and narrow boundaries.

Non-blocking follow-up

A future change could add full App-level event tests for each state transition; the current geometry/action tests plus the existing keyboard path are sufficient for this scoped change.

Merge recommendation

Ready after the draft is marked ready and an independent reviewer records approval. This account authored the PR, so GitHub will not allow it to self-approve.