Refactor arm UDP controller with user-space height coordinates and gripper toggle

- Switch height to user coordinates (0=top, 290=bottom mm), invert sign
  internally for UDP protocol
- Replace raw --j5 arg with --up flag (gripper up/down toggle)
- Add default geometry constants (L1, L2, X4, Z4) and gripper
  open/closed angles
- Update --show-fk and pose mode to derive Z4 from gripper state
- Add mm unit annotations to all CLI help text and output
- Update cached joint state to match new coordinate convention
- Add camera_capture.py: single-shot JPEG grabber from ESP32 MJPEG stream
- Fix missing newline at EOF in craic.md

tools/.udp_control_state.json

@@ -1,8 +1,8 @@
 {
-  "height": -252,
-  "j2": 40,
-  "j3": 64,
-  "j4": -69,
-  "j5": 81,
+  "height": -290,
+  "j2": -66,
+  "j3": 145,
+  "j4": -44,
+  "j5": -100,
   "j6": 0
 }