feat: remember each view's selection and scroll position across navigation

[Bccorb]

Problem

selected_row and scroll_offset are a single shared pair, and on_view_enter resets both to the top on every view switch. Navigating away from a list and back always drops the operator at row one, losing their place. On a long EC2 or Secrets list that is a real cost when pivoting between views during triage.

Context

#31 closed the correctness half of this (no view can hold an out-of-bounds selection) by centralizing the clamp in the shared list helper from #30. It deliberately did not add persistence, because the acceptance there was about out-of-bounds selection and on_view_enter resetting to the top meant there was no cross-view bleed to fix.

Proposed fix

Keep per-view selection state, for example a map from ActiveView to its (selected_row, scroll_offset), restored on view enter and cleared alongside the inventory on a profile or region change (the same point where clear_service_data runs, so a restored cursor can never point into another account's data).

ui::views::list_table::render_list_table already takes the selection as &mut borrows, so views would pass the per-view entry instead of the shared fields with no change to the helper.

Acceptance

• Leaving a view and returning restores the previous selection and scroll position
• Selection state is cleared on a profile or region change
• A restored selection is still clamped when the underlying list shrank

[Bccorb]

Re-checked against current main. Not done — selection and scroll are still a single global pair on App, zeroed by on_view_enter on every view switch.

One design point to settle before implementing, because a neighbouring decision deliberately went the other way: the row filter added in #39 is intentionally cleared on view switch, so a query typed against EC2 cannot silently hide rows in Lambda. If selection and scroll become per-view, it is worth deciding explicitly whether the filter follows the same rule or stays view-scoped, rather than having the two diverge by accident.

Also note the epic (#45) lists #31 as "per-view selection state". That is a misdescription: #31 centralized selection clamping into the shared list helper. Remembering a selection across navigation is this issue, and it has never been implemented.