fix(notifications): clean up NotificationPage and keep the info panel in sync with selection

[gmmcosta15]

Description

Select the type:

• Feature
• Bug fix
• Code refactor
• Documentation

Cleans up NotificationPage and fixes several cases where the info panel (Type/Time) fell out of sync with what's actually selected in the list.

• Renamed leftover update_* widget/method names to notification_*.
• Dropped the dead on_update_message signal and unused cli_tracking deque.
• Notifications now insert newest-first (top of list) instead of appending at the bottom.
• Fixed EntryDelegate.prev_index drift: since new notifications now prepend instead of append, every existing row shifts down on insert, prev_index (used to know which row's highlight to clear) is now kept valid via a rowsInserted handler.
• The topmost notification is now auto-selected (info panel populated) on panel open and whenever a new notification arrives.Previously the user had to click it once before its data would show.
• Fixed the expand/collapse arrow: clicking it only toggled the row's expanded state and returned early, so it never called item_selected.
• Fixed duplicate-message collapsing (refresh_last_if_duplicate): the cached timestamp bumped correctly, but if that item was currently shown in the info panel, its Time label stayed frozen at the first occurrence. It's now refreshed too.
• Fixed "Delete all" / "Delete" leaving stale info-panel state: Type/Time kept showing the last-viewed (now-deleted) notification and the Delete button stayed enabled pointing at nothing. Deleting now re-selects the new top item, or resets the info box if the list is empty.
• Fixed EntryListModel.setData(ExpandRole) never returning True, violating Qt's setData contract.
• Increased spacing between the left icon and text for all list-based pages (universal constant in the shared delegate — wifi/network, files, spoolman, filament, notifications).

Motivation

NotificationPage still carried dead code and naming from when it was the Update page. While reordering to newest-first, several latent bugs in the shared list delegate's click/selection handling surfaced (or became user-visible for the first time, since the newest/topmost item is now the first thing a user sees and clicks).

Tests

• tests/util/test_notification_page_unit.py updated for the renamed widgets, all 4 tests pass.