Improve Items tab width, filtering, sorting, and item icons

[AdamZ-8113]

Description of the problem being solved:

The Items tab's All Items area is cramped and its existing Sort action permanently rewrites the build's item order. It also lacks quick ways to filter and inspect larger item collections, and newly added items can remain hidden by the current view.

This PR:

• Repositions and widens the All Items area to 450px while retaining responsive portrait and landscape layouts
• Makes the Equipment item list slightly wider to accommodate increasingly longer item names (Foulborn, Vestigial, etc.)
• Adds item sorting based on Item Slots, Name, Rarity, and Loadout
• Makes Custom Order the default (preserving existing functionality sort of) and treats Item Slot, Name, Rarity, and Loadout sorting as non-destructive views over that order;
• Adds Item Slot and Loadout filters
• Adds Search
• Groups the Loadout view while distinguishing items used outside complete Loadouts from unused items;
• Keeps drops from sorted views safe by appending them to Custom Order;
• Auto focuses / navigates to newly added items across the relevant add/equip/drag paths
• Updates the Items-tab help text and Shared Items empty-state text for the wider layout
• Changes the Delete Unused/All/Delete buttons to match the size and format of other "action" buttons
• Made micro spacing changes on the page (row break between "all items" and "unique items" lists are now 20px, matching the same spacing as the width between columns)
• Adds slot icons to the Item Database and All Items lists through a shared icon module already used by the Skills list

The icon work forward-ports Simone's work from #7265 (original commit f6a892a39109a9c591625bf85d35c09913c5004b). The two PNG assets are byte-identical to Simone's originals; the implementation is adapted to the current class/module structure and the new loadout group headers.

Steps taken to verify a working solution:

• docker compose run --rm --no-deps busted-tests busted --lua=luajit -p TestItemDBControl_spec.lua: 5 successes, 0 failures, 0 errors.
• docker compose run --rm --no-deps busted-tests busted --lua=luajit -p TestItemListControl_spec.lua: 20 successes, 0 failures, 0 errors.
• Complete suite: 585 successes, 0 failures, and 1 pre-existing error in unchanged spec/System/TestItemParse_spec.lua:1362.
• git diff --check upstream/dev..HEAD passes.

The complete-suite error comes from new("Item", raw) in the test added by commit d815ced0dfd17b443ba83ccda0dac812cb4068fb / #10174. Current class construction requires new("Item"):Item(raw). This PR does not modify that test, Modules/Common.lua, or Classes/Item.lua; the unrelated test was intentionally left unchanged to keep this PR scoped.

Link to a build that showcases this PR:

Not applicable; this is an Items-tab UI and list-management change.

Before screenshot:

After screenshot: