fix: resolve Pydantic Literal error preventing pipeline execution

The Run model used a strict Literal['baseline', 'explore', 'validate', 'wfv', 'oos']
for the phase field, but the new pipeline emits phases like 'phase1', 'phase2', etc.
This resulted in a silent validation failure inside the pipeline loop before MT5
was launched, causing the optimizer to appear 'stuck' without ever opening MT5.

Fixed by relaxing the phase field to 'str'.

data/models.py

@@ -100,7 +100,7 @@ class Run(BaseModel):
     period_start:  str
     period_end:    str
     params:        dict[str, Any]           # snapshot of all EA inputs used
-    phase:         Literal["baseline", "explore", "validate", "wfv", "oos"]
+    phase:         str
     hypothesis_id: Optional[str] = None
     tester_model:  int = 0                  # 0=Every Tick
     ini_snapshot:  Optional[str] = None     # full .ini content for reproducibility