Add a ring size option

[PyFlat-JR]

What does this PR do?

Adds a ring size option to the tile and to the panel's rings layout.

• Ring size (%), a slider from 50 to 100 in steps of 5. The default 100 is today's size, so existing widgets don't change.
• The ring fills its slot and its diameter only sizes the parts, so a smaller ring caps its frame (MaxWidth/MaxHeight) at the scaled diameter and sizes the stroke, bolt, icon and text from that. At 100 % the frame stays uncapped.
• On the wide tile the details get the freed space.
• Hidden for the list layout, which has no ring.
• New previews: "Tile - smaller ring", "Panel - smaller rings".

Checklist

• I have read AGENTS.md and CONTRIBUTING.md.
• dotnet build and dotnet test pass locally (0 warnings, 254 tests).
• I updated README.md / AGENTS.md if this changes what they describe.
• If this touches a device backend: I tested it against the real hardware (see below).

Device/hardware tested against (if applicable)

Not a device backend.