fix(frontend): throttle teleop websocket commands

[xiaolefang-dm]

Summary

• throttle joystick teleop WebSocket sends to 10 Hz
• coalesce high-frequency pan updates into the latest command
• force immediate zero command on joystick release / emergency stop

Context

Using the frontend joystick while recording rosbags appears to publish cmd_vel at very high frequency and can contend with image recording. Limiting teleop sends should reduce backend/DDS/robot-control load while preserving responsive stop behavior.

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.16 s (256.7 files/s, 38275.1 lines/s)

Language	files	blank	comment	code
Python	13	620	262	3464
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	941	360	4961

[xiaolefang-dm]

Closing for now; keeping branch xiaole/fix-teleop-throttle available for testing before opening a PR.

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (244.9 files/s, 36509.3 lines/s)

Language	files	blank	comment	code
Python	13	620	262	3464
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	941	360	4961

[github-actions]

cloc	github.com/AlDanial/cloc v 2.04 T=0.17 s (253.5 files/s, 37797.8 lines/s)

Language	files	blank	comment	code
Python	13	620	262	3464
Markdown	4	155	6	426
C++	4	60	38	409
Bourne Shell	15	41	9	272
Dockerfile	1	31	30	202
JSON	2	8	0	58
TOML	1	4	0	58
make	1	18	15	55
CMake	1	4	0	17
--------	--------	--------	--------	--------
SUM:	42	941	360	4961