Redesign the battery widgets around device rings, colour schemes and a default press action

[PyFlat-JR]

What does this PR do?

Redesigns both deck widgets and moves the plugin to Macro Deck 3.0.0-beta.15.

Widgets

• Each device is drawn as a coloured level ring around a vector icon for its kind (DeviceGlyphs),
  with a bolt in the ring's gap while it charges.
• Panel: a grid of rings that arranges itself to the widget's size and aspect, optionally with
  names and a short trend line under each ring. The list layout is still there as an option, with
  icons, bars and top/centre/bottom alignment. Its rows sit inline and switch to stacked when a name
  or caption would be cut off (UiFirstFit).
• Tile: one large ring; on a wide tile, name, level and state sit beside it.
• Colour schemes: level with cyan while charging (default), level only, green and red, by device
  type, or a smooth gradient. Every scheme shows a level at or below the low-battery threshold in
  red, and a stale one in grey.
• Config form: now split into Devices and Appearance tabs, with segmented controls and an action
  editor beside the properties.

Press behaviour

• Both widget types run the user's own actions (SupportsFlows). Their default Short Press action
  is "Refresh battery levels" (DefaultShortPressAction, Macro Deck PR 1111). A Short Press action
  set by the user replaces it, and actions on other triggers (such as a long press) run alongside it.
• This replaces the earlier workaround, which dropped the tap refresh as soon as any action was bound.

Tooling

• All MacroDeck packages and the release workflow's cli-version are on 3.0.0-beta.15.
• make preview renders every widget preview to PNGs (store images). make pack builds for the
  current platform, and the Makefile forces UTF-8 console output on Windows.

Behaviour changes for existing users

• Rings are the new default layout, so a panel saved before this release opens as rings after the
  update. The list layout is one setting away.
• A host older than 3.0.0-beta.15 ignores the default press action, so a short press does nothing
  there.

Checklist

• I have read AGENTS.md and CONTRIBUTING.md.
• dotnet build and dotnet test pass locally (0 warnings, 221 tests).
• I updated README.md / AGENTS.md if this changes what they describe.
• If this touches a device backend: not applicable, no backend changes.

Device/hardware tested against (if applicable)

Not a device backend change. The widgets were run in Macro Deck on Windows, with no errors found.