Dynamic Surge Pricing for High-Demand Expert Categories

[Luluameh]

Background
During peak hours or high-demand periods (e.g., system outages where dev experts are highly sought), experts should be able to opt into an automated surge pricing model.
Goal
Implement dynamic pricing multiplier calculations based on the category's active session density.
Acceptance Criteria

• Track active sessions per category in persistent storage.
• Surge multiplier: 1.0x up to 2.0x calculated dynamically if active sessions exceed thresholds.
• Seekers must explicitly approve the surge multiplier in start_session.
  Key Files
  contracts/src/lib.rs, contracts/src/reputation.rs