refactor(ml): consolidate 13 duplicate OHLCVBar definitions into single canonical type

Created ml/src/types/ohlcv.rs as the single source of truth for OHLCVBar
(DateTime<Utc> timestamp, f64 OHLCV fields). Replaced all 13 duplicate
definitions across features/, regime/, real_data_loader, and evaluation/
with imports from crate::types::OHLCVBar.

Key changes:
- New: ml/src/types/mod.rs + ohlcv.rs with canonical OHLCVBar
  (derives: Debug, Clone, Copy, PartialEq, Serialize, Deserialize + Default)
- Renamed: evaluation::metrics::OHLCVBar → OHLCVBarF32 (genuinely
  different type: f32 fields, i64 timestamp for compact backtesting)
- Eliminated all import aliases (ExtractionOHLCVBar, RegimeOHLCVBar,
  PriceOHLCVBar, VolumeOHLCVBar) in dbn_sequence_loader.rs and pipeline.rs
- Renamed regime::orchestrator::Bar → OHLCVBar (same fields, just aliased)
- Updated 39 files total (13 definitions removed, imports normalized)

1883 lib tests passing, compilation clean.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ml/src/data_validation/corrector.rs

@@ -10,7 +10,7 @@
 //! All corrections are conservative and preserve data integrity.
 //! Original data is never modified in-place.
 
-use crate::real_data_loader::OHLCVBar;
+use crate::types::OHLCVBar;
 use anyhow::Result;
 
 /// Data corrector for automatic fixes

ml/src/data_validation/rules.rs

@@ -4,7 +4,8 @@
 //! Each rule implements the `ValidationRule` trait and can be composed
 //! into a comprehensive validation pipeline.
 
-use crate::real_data_loader::{Indicators, OHLCVBar};
+use crate::real_data_loader::Indicators;
+use crate::types::OHLCVBar;
 use anyhow::Result;
 
 /// Validation error information

ml/src/data_validation/validator.rs

@@ -3,7 +3,8 @@
 //! Orchestrates multiple validation rules and generates comprehensive reports.
 
 use super::rules::{Severity, ValidationError, ValidationRule};
-use crate::real_data_loader::{Indicators, OHLCVBar};
+use crate::real_data_loader::Indicators;
+use crate::types::OHLCVBar;
 use anyhow::Result;
 use std::sync::atomic::{AtomicUsize, Ordering};