Replace resource number spinners with preset dropdowns in container Resources

[Copilot]

The RAM/Swap/Storage editors used a raw number input whose up/down arrows nudged megabyte values by a single step, making it tedious to reach useful sizes like 4096 MB.

Changes

• New ResourceValueInput component — a preset dropdown of common sizes with a Custom… option that reveals a number input for precise editing. MB presets that divide evenly render as whole GB (e.g. 4096 → 4 GB).
• ResourcesSection wiring — added per-resource presets and bumped the custom-edit step to multiples of 1024 (RAM/Swap) and 10 (RootFS); swapped the inline number input for ResourceValueInput.

Presets: RAM 256 MB–32 GB, Swap 0 MB–16 GB, CPUs 1–32, RootFS 5–500 GB.

<ResourceValueInput
  label={opt.label}
  unit={opt.unit}
  min={opt.min}
  step={opt.step}
  presets={opt.presets}
  value={editValue}
  onChange={setEditValue}
/>

The editable number field is retained via Custom…, so arbitrary values are still supported. Both the dropdown and input carry ARIA labels.