Enhance API with data loading functionality and update README.

- Added `/load-data` endpoint to load transaction data from either a database or a CSV file.
- Updated `SalaryAnalyticsPipeline` and `DataLoader` to support loading from CSV.
- Implemented data validation and error handling for loading processes.
- Revised README to include new data loading instructions and workflow steps.
- Added checks to ensure data is loaded before running analysis endpoints.

salary_analytics/consistent_amount_analyzer.py

@@ -40,12 +40,18 @@ class ConsistentAmountAnalyzer:
         if cv_threshold is None:
             cv_threshold = MODEL_CONFIG['cv_threshold']
 
-        self.df = self.df.groupby('accountid').apply(
+        # Create a copy of the original DataFrame
+        self.const_df = self.df.copy()
+        
+        # Calculate consistent amount flags
+        consistent_flags = self.const_df.groupby('accountid').apply(
             lambda group: self.flag_consistent_amounts(group, cv_threshold)
         ).reset_index(level=0, drop=True)
-
-        self.const_df = self.df.copy()
-        return self.df
+        
+        # Add the flags to the original DataFrame
+        self.const_df['is_consistent_amount'] = consistent_flags
+        
+        return self.const_df
 
     def get_consistent_amount_data(self):
         """Get transactions identified as having consistent amounts."""