Define Telemetry Data Schema & Performance Deviation Metrics

** Description
We need a documented, agreed-upon schema for pilot telemetry before any pipeline work starts. Real flight data from Dr. Gajapriya isn't available yet, so this issue works from the existing repo's plugin output structure and the client's stated requirements (altitude, heading, vertical airspeed, airspeed — designated vs. actual). This schema becomes the contract every downstream script depends on.

** Tasks

• Review the current plugin's output format in the repo and document actual field names/types
• Define the deviation formula for each metric (e.g. deviation = actual − target) for altitude, heading, vertical speed, airspeed
• Define pilot metadata fields needed (certification level, flight hours, pilot rating) and how they'll be joined to telemetry
• Write up the schema as a markdown doc in /docs
• Flag any fields the plugin doesn't currently emit but that the client's requirements need

** Acceptance Criteria

• A schema document exists in the repo listing every field, its type, and its source (plugin vs. metadata)
• Deviation formulas are written out explicitly for all four flight-dynamics metrics
• Gaps between what the plugin outputs today and what's needed are called out, not silently assumed