Add parametric 3D-printable enclosure (OpenSCAD)

A printable reimagining of the wooden Kidsbox: rectangular cabinet with two
front speakers, removable top lid (NFC tag rests there, reader mounts beneath),
and swappable speaker mounts.

- kidsbox.scad: master model + part dispatcher (body/lid/speaker_adapter/grill)
- params.scad: all tunable dimensions in one place
- lib.scad: helper modules (rounded shell, bosses, bolt circles)
- Fixed front-panel speaker interface + swappable adapter so any driver fits
  by printing a new adapter (edit spk_* params, re-export)
- Internal mounts: 2x18650 cradle, ESP32-LyraT standoffs, RC522 under lid,
  3 buttons on lid, USB/charge + power-switch side ports, back-wall vents
- Snap-in speaker grills
- Makefile to export STLs and render previews (headless via xvfb)
- Exported STLs and preview renders included
- Link enclosure from main README

Dimensions are sensible defaults from the reference photos and common parts;
README flags the fit-critical values to verify before mass-printing.

https://claude.ai/code/session_01MhAnh68DPNnTjcKqjNYDmk

enclosure/params.scad

@@ -0,0 +1,96 @@
+// ============================================================================
+//  Kidsbox enclosure — parameters
+//  All dimensions in millimetres. Edit here, then re-export the STLs.
+//  See README.md for the export commands.
+// ============================================================================
+
+// ---- global print settings ------------------------------------------------
+$fn            = 64;     // facet count for curves (raise for final render)
+wall           = 3.0;    // shell wall thickness
+floor_t        = 3.0;    // bottom thickness
+corner_r       = 6.0;    // outer vertical-edge radius
+fit            = 0.30;   // general clearance for mating parts (per side)
+
+// ---- outer box dimensions (interior is derived) ---------------------------
+box_w          = 190;    // width  (X) — roughly one banana, per reference photo
+box_h          = 110;    // height (Z)
+box_d          = 115;    // depth  (Y)
+
+// derived interior
+inner_w        = box_w - 2*wall;
+inner_d        = box_d - 2*wall;
+inner_h        = box_h - floor_t;   // open-top shell, lid closes it
+
+// ---- lid -------------------------------------------------------------------
+lid_t          = 2.4;    // thin enough for 13.56 MHz NFC to read through PLA
+lid_rim_h      = 6.0;    // depth of the lip that drops into the box
+lid_rim_t      = 1.6;    // thickness of that lip
+lid_screw_d    = 3.2;    // M3 clearance
+lid_boss_d     = 9.0;    // corner screw-boss outer diameter
+lid_boss_inset = 9.0;    // boss centre inset from interior corner
+
+// ---- speaker panel interface (FIXED) --------------------------------------
+//  This is the standard "mount for the speaker mount". Every swappable
+//  speaker adapter bolts to THIS pattern, so the box never changes.
+spk_sound_d      = 66;   // sound opening through the front panel
+spk_bolt_d       = 80;   // bolt circle for the adapter screws
+spk_bolt_count   = 4;    // number of adapter screws
+spk_bolt_hole_d  = 3.2;  // M3 clearance through the panel
+spk_boss_d       = 8.0;  // screw boss diameter on the inside of the panel
+spk_boss_h       = 5.0;  // screw boss height (into the box)
+spk_spacing      = 94;   // centre-to-centre of the two speakers (X)
+spk_center_z     = 48;   // speaker centre height from the box floor (Z)
+
+// ---- swappable speaker ADAPTER (edit for YOUR speaker) ---------------------
+//  Print one adapter per speaker model. Defaults suit a common 3" driver.
+adapter_t        = 3.0;  // adapter plate thickness
+adapter_outer_d  = 88;   // outer diameter of the adapter disc
+spk_frame_d      = 66;   // speaker outer frame diameter (seat recess)
+spk_frame_seat   = 1.5;  // depth the frame sinks into the adapter
+spk_cutout_d     = 58;   // cone clearance hole through the adapter
+spk_screw_count  = 4;    // the SPEAKER's own mounting holes
+spk_screw_bolt_d = 60;   // bolt circle of the speaker's mounting holes
+spk_screw_d      = 3.0;  // speaker screw clearance
+
+// ---- speaker grill (snaps into the sound opening) -------------------------
+grill_t          = 2.4;  // grill face thickness
+grill_rings      = 3;    // number of concentric rings
+grill_spokes     = 6;    // number of radial spokes
+grill_lip_h      = 5.0;  // snap lip depth into the sound hole
+grill_standoff   = 3.0;  // gap the grill holds off the cone
+
+// ---- buttons (top lid, row near the front edge) ---------------------------
+//  Kept off the front face (which stays clean like the reference box) and
+//  clear of the central NFC reader, which sits under the lid centre.
+btn_d            = 12.2; // panel hole for a 12 mm momentary switch
+btn_count        = 3;    // vol-, play/pause, vol+
+btn_pitch        = 26;   // spacing between buttons along X
+btn_row_y        = 18;   // distance of the button row from the front wall
+
+// ---- side ports ------------------------------------------------------------
+usb_w            = 12;   // micro-USB / charge access cutout (W)
+usb_h            = 7;    // (H)
+usb_center_z     = 22;   // height of the port from the floor
+sw_d             = 7;    // power slide-switch hole diameter
+sw_center_z      = 22;
+
+// ---- ESP32-LyraT v4.3 mount (verify against your board) -------------------
+lyrat_w          = 99;   // board long edge
+lyrat_d          = 57;   // board short edge
+lyrat_hole_dx    = 92;   // mounting-hole rectangle, long axis  (VERIFY)
+lyrat_hole_dy    = 50;   // mounting-hole rectangle, short axis (VERIFY)
+lyrat_standoff_h = 6;    // standoff height off the floor
+lyrat_standoff_d = 6;    // standoff outer diameter
+lyrat_screw_d    = 2.6;  // self-tap for M2.5/M3
+
+// ---- 2x 18650 battery holder cradle ---------------------------------------
+batt_holder_w    = 78;   // typical 2-cell holder footprint (X)
+batt_holder_d    = 39;   // (Y)
+batt_holder_h    = 21;   // (Z)
+batt_wall        = 2.0;  // cradle wall
+batt_clip        = true; // add retaining clips
+
+// ---- ventilation -----------------------------------------------------------
+vent_slot_w      = 3;
+vent_slot_len    = 28;
+vent_count       = 5;