Add configurable entity tile rounding and continuous outlines

[XJle6uIIIeK]

Entity regions can now use continuous rounded tile and outline contours. bc_entities_rounding sets the radius from 0% (square) to 100% (a circle for an isolated tile), and bc_entities_rounding_mode selects outer corners (0), inner corners (1), or both (2). The settings are also exposed under Tile Outlines.

The tile mesh and outlines share category and layer boundaries. Covered material junctions fill the exposed area with the neighboring asset. Through-hook tiles retain rounding and continue their stripe texture into inner wedges; straight outline bands meet adjacent arcs without gaps or corner spurs. Teleporter labels use a consistent size across a rounded region. Floating-point UVs are supported by the buffered OpenGL/Vulkan paths and the legacy unbuffered renderer. Collision and prediction are unchanged.

Screenshots

Through-hook texture restoration and continuous outlines, 100% combined rounding:

Consistent labels at a teleporter junction:

77% radius

Checklist

• Tested the change ingame
• Provided screenshots if it is a visual change
• Tested in combination with possibly related configuration options
• Written a unit test (especially base/) or added coverage to integration test
• Considered possible null pointers and out of bounds array indexing
• Changed no physics that affect existing maps
• Tested the change with ASan+UBSan or Valgrind's memcheck (optional)
• I didn't use generative AI to generate more than single-line completions

AI was used to implement the feature and regression fixes, resolve upstream merge conflicts, and run the build, tests and visual/performance checks. The results and unedited screenshots are documented above.