Joints: gears, rack and pinion, and screws (#1524)

Motion links can carry a coupling (gear pair, rack and pinion, screw) whose ratio follows radii, picked round faces or pitch. Design format 23.

Co-authored-by: SychPL <SychPL@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

assets/locales/de.json

@@ -760,6 +760,9 @@
   "cmd.joint_limits": "Gelenkgrenzen",
   "cmd.joint_list": "Gelenke auflisten",
   "cmd.joint_motion_link": "Bewegungsverknüpfung",
+  "cmd.joint_gear": "Zahnrad",
+  "cmd.joint_rack_pinion": "Zahnstange und Ritzel",
+  "cmd.joint_screw": "Schraube",
   "cmd.joint_origin": "Gelenkursprung",
   "cmd.joint_rigid_group": "Starrgruppe",
   "cmd.joint_solve": "Gelenke lösen",
@@ -1122,5 +1125,21 @@
   "Min": "Min",
   "Max": "Max",
   "Length": "Länge",
-  "Area": "Fläche"
+  "Area": "Fläche",
+  "coupling.gear_1": "Zahnrad 1",
+  "coupling.gear_2": "Zahnrad 2",
+  "coupling.pinion": "Ritzel",
+  "coupling.rack": "Zahnstange",
+  "coupling.nut": "Mutter",
+  "coupling.radius_1": "Radius 1",
+  "coupling.radius_2": "Radius 2",
+  "coupling.internal": "Innenzahnrad",
+  "coupling.pitch": "Steigung",
+  "coupling.picked": "gewählt",
+  "coupling.not_round": "keine runde Fläche",
+  "coupling.gear_1_pick": "Zahnrad 1 (optional)",
+  "coupling.gear_2_pick": "Zahnrad 2 (optional)",
+  "coupling.pinion_pick": "Ritzel (optional)",
+  "coupling.needs_turns": "braucht zwei Gelenke, die sich drehen",
+  "coupling.needs_turn_and_slide": "braucht ein Gelenk, das sich dreht, und eines, das gleitet"
 }