feat(web): keyboard row navigation on five more list pages - #2572

🟢 Confidence 10/10 · safe to merge. Scene tests pin stepping, Enter and Escape on all five pages; only the scroll command's DOM effect is unproven.
_{no findings · tests covered · risk medium}

Extracts one shared row-keyboard module and row-focus look, moves the traces list onto it and gives J/K/arrows/Enter/Escape to five more list pages. Behaviour is unchanged where it should be, and each page's focusable list matches the rows it draws.

• list-keys.ts: one document key stream, pure focus step, key-to-action map and scroll command
• row-focus.ts: data-focused / data-list-row marker and look, drawn by tableRow, listRow, gridListRow and selectableRow
• Services, metrics table, investigations, dashboards and the alerts inbox adopt the list keys
• Dashboards and the alerts inbox keep the focused row by id; the traces list moves onto the shared stream

_{7c2189e · Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}