Dig marks and hover follow the real block shape; sprites no longer clipped by walls behind them

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

DESIGN.md

@@ -16,10 +16,10 @@ An original dungeon management game (genre: dungeon building & defence) that run
 - Camera **freely rotatable 360° and tiltable**
 - Walls with an **irregular surface** (noise displacement of the wall faces, seamless between neighbours)
 - Textures: **procedural pixel art** (tile atlas)
-- Units: **pixel sprites as billboards** (always facing the camera)
+- Units: **pixel sprites as billboards** (always facing the camera), pulled towards the camera in depth so walls behind a unit never cut into its sprite
 - Lighting: **dark + torches** – dark base level; claimed areas and light sources (torches, core, portal, gate) are bright, flickering light
-- **Dig marking**: a marked block glows as a translucent yellow box with a yellow outline around all edges
-- **Hover**: the wall block under the mouse gets a faint version of that box (in the colour of the active tool); while dragging a dig rectangle, every block inside is tinted faintly; floor tiles get an outline
+- **Dig marking**: a marked block glows yellow along its **real irregular shape** (tinted top and open sides, outline following the displaced edges)
+- **Hover**: the wall block under the mouse gets a faint version of that highlight (in the colour of the active tool); while dragging a dig rectangle, every block inside is tinted faintly; floor tiles get an outline
 - **Tile outlines**: subtle dark lines around every tile (floors, wall tops, vertical wall edges), following the irregular surface; toggle with G (later in the graphics settings)
 - The UI is a 2D layer on top, including a minimap