feat(case): relieve the bracket and foam for the FPC U-turn

The flex leaves the glass's back plane on the left and must fold ~180 deg
to dive into the cavity toward the breakout. A safe bend radius makes
that loop ~4 mm deep, too deep for the 1 mm foam gap, so it fouled the
rigid bracket. Open the bracket's left frame member and the foam's left
border over the FPC span, aligned with the body's existing slot, to give
the U-turn room. Re-adds the relief dropped in c4320e2, correctly scoped.

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 the left edge is relieved to give the FPC room to U-turn into the cavity](renders/bracket.png)
 
 ### Boards (the baseplate is the chassis)