Diagonals: streets, walls, fences, hedges and house walls at any angle

Object frames turn by any angle (quarter turns stay exact, so scenes along
the axes render byte for byte as before); a box in a turned frame is a
prism with its own corners. Rotation is kept as given (normalised to
0..360), no longer snapped to quarter turns.

Depth sort: sprites whose plan outline is not their box carry their convex
outline; when boxes overlap, an outline edge that separates two sprites
orders them. A long diagonal wall sorts right against both sides.

Joints (line_meet, end_cut, cut_box in util.rhai): where a piece off the
axes is involved, corners are mitred and T-junctions slanted; fences put a
corner post or pillar in its own sprite and mitre stone bases; Y joints let
the lowest id run through. Streets: every end part is a cut e + k*w, so
side streets come in at any angle (slanted sidewalk gaps), two streets meet
in a mitre with seam patches; fixes a curve's outer sidewalk that was
skipped when its kerb and back lines had different point counts.

Studio: runs and drags keep to x/y or snap to 45 degree diagonals, Ctrl
gives any angle; a road run turning 45 degrees gets a 45 degree curve;
Rotation is a number box. Streets demo: a diagonal lane with a hedge.
MCP guidance, SCRIPTING/README/ROADMAP.

Tests: Rust 76, Studio and web checks green.

docs/ROADMAP.md

@@ -68,7 +68,8 @@ Each phase ends with tests, a Studio/viewer check in Edge, commit and push.
       (hover preview) and move, turn, copy and delete with them, new parts land on the storey
       shown, collapsible palette that scrolls on its own
 - [x] `examples/house` (a furnished house built from parts), House demo in the web Studio
-- [ ] Openings across two walls; diagonal walls; floor openings for stairs
+- [x] Diagonal walls (any angle, mitred corners, windows and doors on them)
+- [ ] Openings across two walls; floor openings for stairs
 
 ## Backlog (2026-10)
 
@@ -81,6 +82,8 @@ Each phase ends with tests, a Studio/viewer check in Edge, commit and push.
 7. ~~Roundabouts~~ (done, see below)
 8. Waypoint animation: a person or car moving along a path of waypoints
 9. ~~Build your own house~~ (done, see above)
+10. ~~Diagonal streets, walls, fences, hedges~~ (done, see below)
+11. Wildlife and nature: deer, bushes, beehives and more
 
 Done since: the middle mouse button only moves the camera; fences and site walls join like house
 walls (`line_joint`); fence designs (mesh, wood, bars, half stone, cobble, brick with pillars);
@@ -119,6 +122,16 @@ apron (tree, grass or paved). A road run drawn corner by corner gets a curve in
 meta `corner`). Tooltips list the streets each one meets. New `polyline` primitive (open paths, so
 dashes run on round curves). `examples/streets`, Streets demo in the web Studio.
 
+Diagonals: object frames turn by any angle (quarter turns stay exact, so scenes along the axes
+draw as before, byte for byte). Roads, walls, fences, hedges and house walls run at any angle;
+where a piece off the axes meets another, corners are mitred and T-junctions slanted
+(`line_meet`, `cut_box`), fence corners get a post or pillar of their own, side streets come in at
+a slant and open the sidewalk along them, two streets meet in a mitre. The depth sort orders
+sprites whose plan outline is not their box by outline edges, so a long diagonal wall sorts right
+against everything on either side. Studio: runs and drags keep to x or y or go diagonal at 45°
+(Ctrl: any angle), a road run turning 45° gets a 45° curve, Rotation takes any angle. The
+streets demo has a diagonal lane.
+
 ## Phase 2: richer editing
 
 - [x] Interior prefabs (see Build your own house); a building `rooms` prop is still open