feat(case): cut an FPC ribbon relief into the bracket frame

Gap in the left frame member aligned with the body's FPC clearance so
the flex folds back through the bracket plane into the cavity instead
of being pinched. Refresh renders and the bracket alt-text.

hardware/case/README.md

@@ -101,7 +101,7 @@ foam+bracket; the bracket is what stops it dropping _into_ the cavity
 
 ![Midline section: glass clamped between the front lip and the rear foam + bracket; the internal FPC clearance is hidden below the left bezel, standoffs on the cavity floor](renders/section.png)
 
-![The screwed bracket — four corner holes, window clears the active area](renders/bracket.png)
+![The screwed bracket — four corner holes, window clears the active area, and a gap in the left edge lets the FPC fold back into the cavity](renders/bracket.png)
 
 ### Boards (the baseplate is the chassis)
 

hardware/case/typoena-case.scad

@@ -232,7 +232,15 @@ module bracket() {
     ow = P_w + 18; oh = P_h + 18;
     difference() {
         linear_extrude(bracket_t)
-            difference() { rrect(ow, oh, 4); rrect(A_ap_w+2, A_ap_h+2, 2); }
+            difference() {
+                rrect(ow, oh, 4);
+                rrect(A_ap_w+2, A_ap_h+2, 2);
+                // ribbon (FPC) relief: a gap in the LEFT frame member, lined up
+                // with the body's FPC clearance so the flex can fold back through
+                // the bracket plane into the cavity instead of being pinched
+                translate([-(ow + A_ap_w+2)/4, 0])
+                    square([(ow - (A_ap_w+2))/2 + 4, fpc_w], center=true);
+            }
         for (bx=[-(P_w/2+5), P_w/2+5], by=[-(P_h/2+5), P_h/2+5])
             translate([bx, by, -1]) cylinder(h=bracket_t+2, r=1.45);   // M2 clear
     }