feat(pose)!: use coco17 3d router features

Enhance UnknownExercise class with debug data handling and add test for manual unknown exercise in pipeline

refactor(exercises): route pipeline through exercise objects

Implement frame-level issue markers

refactor(exercises): introduce exercise strategies

feat(rep_counter): implement exercise-specific rep counters for push-ups, shoulder presses, and squats; add dependency on fastapi

feat(rep): implement deterministic exercise rep segmentation