fix: resolve critical safety and concurrency issues

[zbzhu99]

Safety fixes:

• Enable Gello joint position and velocity safety clipping (was disabled)
• Fix Franka FR3 clear_error() referencing wrong object (robot_c -> robot)
• Fix Franka disconnect() missing gripper null check before deletion
• Fix UR5 clear_error() missing null check for robot_c
• Fix UR5 reset_to_init/move_to_joint_positions missing init_qvel default
• Fix UR5 gripper null check in reset_to_init()

Concurrency fixes:

• Add thread-safe locks to SharedMemoryQueue put/get/get_k/get_all methods
• Add thread-safe lock to SharedMemoryRingBuffer put method
• Fix timestamp consistency in ring buffer (use same time value)

Stability fixes:

• Add 5-second timeout to state_thread.join() to prevent process hang
• Replace bare except with specific Exception types in xarm6 and ur5