Function computeStakeholderInfluenceTrajectory

Compute the influence trajectory for a stakeholder based on their current score, committee engagement, and comparison to historical baseline.

Trajectory logic:

• If current score > historical by ≥ 5 points AND has committee/rapporteur roles → rising
• If current score < historical by ≥ 5 points → declining
• Otherwise → stable

Confidence depends on whether historical data is available and role count.