refactor: slim pathways.db from 351 MB to 3.5 MB by removing unused tables

Drop fact_interventions (440K rows), mv_patient_treatment_summary (35K rows),
ref_drug_snomed_mapping (144K rows), and processed_files — all unused since
the app moved to pre-computed pathway_nodes.

Key changes:
- Rewrite load_data() to source from pathway_nodes + pathway_refresh_log
- Remove 7 dead methods and 8 dead state vars from pathways_app.py
- Delete patient_data.py, load_snomed_mapping.py, test_large_dataset_performance.py
- Remove SQLiteDataLoader (depended on fact_interventions)
- Remove file tracking schema (processed_files tracked fact_interventions loads)
- Remove legacy diagnosis functions from diagnosis_lookup.py
- Add source_row_count migration for pathway_refresh_log
- Clean all cross-references in __init__.py, data_source.py, migrate.py

data_processing/__init__.py

@@ -24,15 +24,6 @@ from data_processing.schema import (
     REF_DRUG_DIRECTORY_MAP_SCHEMA,
     REF_DRUG_INDICATION_CLUSTERS_SCHEMA,
     REFERENCE_TABLES_SCHEMA,
-    # Fact table schemas
-    FACT_INTERVENTIONS_SCHEMA,
-    FACT_TABLES_SCHEMA,
-    # Materialized view schemas
-    MV_PATIENT_TREATMENT_SUMMARY_SCHEMA,
-    MATERIALIZED_VIEWS_SCHEMA,
-    # File tracking schemas
-    PROCESSED_FILES_SCHEMA,
-    FILE_TRACKING_SCHEMA,
     # Combined schema
     ALL_TABLES_SCHEMA,
     # Reference table functions
@@ -40,16 +31,6 @@ from data_processing.schema import (
     drop_reference_tables,
     get_reference_table_counts,
     verify_reference_tables_exist,
-    # Fact table functions
-    create_fact_tables,
-    drop_fact_tables,
-    get_fact_table_counts,
-    verify_fact_tables_exist,
-    # File tracking functions
-    create_file_tracking_tables,
-    drop_file_tracking_tables,
-    get_file_tracking_counts,
-    verify_file_tracking_tables_exist,
     # Combined functions
     create_all_tables,
     drop_all_tables,
@@ -81,27 +62,12 @@ from data_processing.reference_data import (
 from data_processing.loader import (
     DataLoader,
     FileDataLoader,
-    SQLiteDataLoader,
     LoadResult,
     get_loader,
     REQUIRED_COLUMNS,
     OPTIONAL_COLUMNS,
 )
 
-# Patient data migration functions
-from data_processing.patient_data import (
-    PatientDataLoadResult,
-    load_patient_data,
-    get_patient_data_stats,
-    list_processed_files,
-    calculate_file_hash,
-    # Materialized view functions
-    MVRefreshResult,
-    refresh_patient_treatment_summary,
-    get_patient_summary_stats,
-    verify_mv_consistency,
-)
-
 # Snowflake connector
 from data_processing.snowflake_connector import (
     SnowflakeConnector,
@@ -165,15 +131,6 @@ __all__ = [
     "REF_DRUG_DIRECTORY_MAP_SCHEMA",
     "REF_DRUG_INDICATION_CLUSTERS_SCHEMA",
     "REFERENCE_TABLES_SCHEMA",
-    # Fact table schemas
-    "FACT_INTERVENTIONS_SCHEMA",
-    "FACT_TABLES_SCHEMA",
-    # Materialized view schemas
-    "MV_PATIENT_TREATMENT_SUMMARY_SCHEMA",
-    "MATERIALIZED_VIEWS_SCHEMA",
-    # File tracking schemas
-    "PROCESSED_FILES_SCHEMA",
-    "FILE_TRACKING_SCHEMA",
     # Combined schema
     "ALL_TABLES_SCHEMA",
     # Reference table functions
@@ -181,16 +138,6 @@ __all__ = [
     "drop_reference_tables",
     "get_reference_table_counts",
     "verify_reference_tables_exist",
-    # Fact table functions
-    "create_fact_tables",
-    "drop_fact_tables",
-    "get_fact_table_counts",
-    "verify_fact_tables_exist",
-    # File tracking functions
-    "create_file_tracking_tables",
-    "drop_file_tracking_tables",
-    "get_file_tracking_counts",
-    "verify_file_tracking_tables_exist",
     # Combined functions
     "create_all_tables",
     "drop_all_tables",
@@ -216,22 +163,10 @@ __all__ = [
     # Data loader abstractions
     "DataLoader",
     "FileDataLoader",
-    "SQLiteDataLoader",
     "LoadResult",
     "get_loader",
     "REQUIRED_COLUMNS",
     "OPTIONAL_COLUMNS",
-    # Patient data migration
-    "PatientDataLoadResult",
-    "load_patient_data",
-    "get_patient_data_stats",
-    "list_processed_files",
-    "calculate_file_hash",
-    # Materialized view functions
-    "MVRefreshResult",
-    "refresh_patient_treatment_summary",
-    "get_patient_summary_stats",
-    "verify_mv_consistency",
     # Snowflake connector
     "SnowflakeConnector",
     "SnowflakeConnectionError",