Add optional swap bar next to the memory chart

[glima]

Problem

The memory sensor only reports RAM. update() refreshed with MemoryRefreshKind::nothing().with_ram() and sampled used_memory() / free_memory(), so swap usage was not visible anywhere in the panel.

Change

Adds a Show swap bar next to chart toggle to the memory settings (off by default). When enabled, a narrow fill bar is drawn beside the memory chart showing the share of swap in use:

• Half the size of a regular chart along the panel's flow direction, so it reads as a companion to the memory chart rather than a second full-size element.
• No text. The memory chart beside it already carries the numbers, and there is not enough room at half width.
• Aspect ratio flips (21×42 / 42×21) for vertical panels so it stays half-size in the direction items are stacked.
• Reuses the memory chart colors (background / graph1 / frame).
• Omitted entirely when the system has no swap configured, so nothing changes for those users.

Swap usage (used / total GB) is also listed on the memory settings page while the toggle is on.

Implementation notes

• svg_graph::bar() is a new standalone renderer: rounded rect, bottom-up fill clipped to the corner radius, 1px frame.
• Memory now also tracks total_swap / swap_used, refreshed via .with_swap() alongside the existing RAM refresh, so no extra syscall pass is added.
• MemoryConfig::show_swap defaults to false, so existing configs deserialize unchanged and the panel looks the same until the toggle is flipped.

Translations

memory-show-swap and swap-explanation were added to every locale file, since all locales in this repo currently carry the full key set. The non-English files get the English string as a placeholder for translators to replace.

Testing

cargo build and cargo clippy are clean (only pre-existing warnings). Verified on a machine with 68 GB of swap that the bar tracks usage, and checked the rendered SVG geometry standalone.

[Hyperchaotic]

Thank you for this PR. I'm thinking about how it looks. I'm wondering if it should be a full secondary chart, like temp is to CPU, the user can then choose between line/ring. @CarsonBurke thoughts?

(In the future, not in the scope of this PR, it would be nice to be able to adjust chart width for line/bar charts and corner radius.)