refactor(dual-franka): separate task policies from robot prompts

[NewYork424]

Description

Keep demo-specific manipulation policies in task definitions rather than shared robot prompts.

• Remove mandatory three-segment VLA, placement staging and advisory joint-recovery rules from shared prompts; retain controller safety.
• Clarify that fixed VLA policy conditioning is not retargeted by the planner's prompt.
• Update Task5 to require the spoon inside the cup, and add Task6 for two-cup dirty/clean sorting without chopsticks or spoons.

Scene-specific camera, ordering and destination requirements remain in the demo tasks. Operator reset and final-verdict requirements are unchanged.

Replaces #259 with the same commits, moving the source branch to the contributor fork. Previous review discussion remains in #259.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.