lid: extend side flanges into Y+ corners (step A)

Extend side flanges and backing ribs from LID_Y_LEN-FLANGE_W+SLIDE_CLEAR
to LID_Y_LEN-SLIDE_CLEAR so they reach the Y+ locking flange region.
Closes the corner gap where neither side nor locking flange had material.

lid.scad

@@ -16,26 +16,26 @@ module lid() {
   // Wide vertical face at x=WALL+FLANGE_W (inner), tip at bottom-wall-face — same
   // (-FLANGE_W, -FLANGE_H) hypotenuse slope as base flanges so they mate when lid slides in.
   color("#2C3863") {
-    // Left (X-) flange — stops at Y+ locking flange inner face
+    // Left (X-) flange — extends into Y+ corner to meet locking flange
     hull() {
       translate([WALL + FLANGE_W - SLIDE_CLEAR - 0.01, 0, 0])
-        cube([0.01, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, FLANGE_H - SLIDE_CLEAR]);
+        cube([0.01, LID_Y_LEN - SLIDE_CLEAR, FLANGE_H - SLIDE_CLEAR]);
       translate([WALL + SLIDE_CLEAR, 0, -0.005])
-        cube([0.01, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, 0.01]);
+        cube([0.01, LID_Y_LEN - SLIDE_CLEAR, 0.01]);
     }
-    // Right (X+) flange — stops at Y+ locking flange inner face
+    // Right (X+) flange — extends into Y+ corner to meet locking flange
     hull() {
       translate([OUT_L - WALL - FLANGE_W + SLIDE_CLEAR, 0, 0])
-        cube([0.01, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, FLANGE_H - SLIDE_CLEAR]);
+        cube([0.01, LID_Y_LEN - SLIDE_CLEAR, FLANGE_H - SLIDE_CLEAR]);
       translate([OUT_L - WALL - SLIDE_CLEAR - 0.01, 0, -0.005])
-        cube([0.01, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, 0.01]);
+        cube([0.01, LID_Y_LEN - SLIDE_CLEAR, 0.01]);
     }
 
     // Interior ribs — 2 mm wide
     translate([WALL + FLANGE_W - SLIDE_CLEAR, 0, 0])
-      cube([2.0, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, FLANGE_H]);
+      cube([2.0, LID_Y_LEN - SLIDE_CLEAR, FLANGE_H]);
     translate([OUT_L - WALL - FLANGE_W + SLIDE_CLEAR - 2.0, 0, 0])
-      cube([2.0, LID_Y_LEN - FLANGE_W + SLIDE_CLEAR, FLANGE_H]);
+      cube([2.0, LID_Y_LEN - SLIDE_CLEAR, FLANGE_H]);
 
     // Y+ locking flanges — angled wedge matching side-flange profile; split around FPC notch
     for (seg = [