Vendor BOSL2 as submodule; convert rounded_box to cuboid()

Also drop dead fpc_adapter references left over in lid.scad (item 9).

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "BOSL2"]
+	path = BOSL2
+	url = https://github.com/BelfrySCAD/BOSL2.git

BOSL2

@@ -0,0 +1 @@
+Subproject commit fbcdfdd511b6abfde93c43c8f85c2bd24ee7a02d

lid.scad

@@ -3,23 +3,10 @@
 include <params.scad>
 use <epd_case.scad>
 use <GDEY0583T81.scad>
-use <fpc_adapter.scad>
 
 /* [Preview] */
 SHOW_DISP = true;
 
-/* [FPC Adapter Mount] */
-ADAPT_SLOT_GAP = 10.0;  // gap: adapter Y+ edge to slot Y- edge ← tune
-
-// Adapter board dimensions (must match fpc_adapter.scad PCB_W / PCB_H)
-_adpt_w = 32.0;
-_adpt_h = 18.0;
-
-// Derived adapter position in lid XY space
-_slot_y    = LID_Y_LEN - 3 - FPC_U_DEPTH + FPC_U_T;  // slot Y- edge
-_adapt_ox  = PCB_OX + FPC_CX - _adpt_w / 2;           // adapter PCB X- edge
-_adapt_oy  = _slot_y - ADAPT_SLOT_GAP - _adpt_h;       // adapter PCB Y- edge
-
 // ============================================================
 //  LID  (slide-on; enters from Y- face, closes toward Y+)
 //  Flanges sit inside cavity and ride on base retention flange hypotenuses.

params.scad

@@ -2,6 +2,7 @@
 //  Shared Parameters
 //  include <params.scad> in all component files
 // ============================================================
+include <BOSL2/std.scad>
 
 /* [Design Style] */
 EPD_IS_LID = true;   // true: epd_case forms the lid ceiling; false: flat ceiling plate
@@ -136,8 +137,8 @@ FPC_CX      = OUT_L/2 - epd_case_w/2 + (_fpc_x1 + _fpc_xw/2) - PCB_OX;
 FPC_U_DEPTH = FPC_U_T - WALL - 3 + (epd_case_d - (BEZEL_Y + DISP_D));
 
 /* [Shared Helper] */
+// Corner-anchored box (origin at the -X,-Y,-Z corner) with rounded vertical edges,
+// matching the pre-BOSL2 hull-of-cylinders convention used throughout this project.
 module rounded_box(l, w, h, r) {
-    hull()
-        for (dx = [r, l-r], dy = [r, w-r])
-            translate([dx, dy, 0]) cylinder(r=r, h=h, $fn=32);
+    cuboid([l, w, h], rounding=r, edges="Z", anchor=BOTTOM+FRONT+LEFT, $fn=32);
 }