Issue #69: T-JEPA pipeline (mask=0.3, EMA 0.996→1.0)

## Task
Implement T-JEPA training pipeline.

## Config
- Mask = 0.3
- EMA = 0.996 → 1.0
- Loss = L2-MSE
- Steps = 20K

## Acceptance Criteria
- T-JEPA training for 20K steps
- EMA schedule 0.996 → 1.0
- L2-MSE loss implementation
- Save checkpoints every 5K steps

## Refs
- EXP-001: Trinity physics

## Commit
"feat(tjepa): implement T-JEPA pipeline (mask=0.3, EMA 0.996→1.0)"  
Ref: EXP-001