Remove investigation feature completely

- Delete investigation CLI command and related services
- Remove investigation data models and report generators
- Clean up configuration options and documentation
- Update gitignore and remove stale egg-info

Investigation feature is no longer needed and has been fully removed.
Backup preserved in git tag 'pre-investigation-removal'.

README.md

@@ -54,8 +54,6 @@ drt validate --config config.yaml
 # 4. Run comparison
 drt compare --config config.yaml
 
-# 5. (Optional) Investigate regression issues
-drt investigate --analysis-dir analysis/output_<TIMESTAMP>/ --config config.yaml
 ```
 
 ## 📦 Platform-Specific Installation
@@ -134,34 +132,6 @@ drt compare --config <CONFIG_FILE> [OPTIONS]
 - `--verbose, -v` - Enable verbose output
 - `--dry-run` - Show what would be compared without executing
 
-### Investigate
-
-Execute diagnostic queries from regression analysis.
-
-```bash
-drt investigate --analysis-dir <ANALYSIS_DIR> --config <CONFIG_FILE> [OPTIONS]
-```
-
-**Options:**
-- `--analysis-dir, -a PATH` - Analysis output directory containing `*_investigate.sql` files (required)
-- `--config, -c PATH` - Configuration file (required)
-- `--output-dir, -o PATH` - Output directory for reports (default: ./investigation_reports)
-- `--verbose, -v` - Enable verbose output
-- `--dry-run` - Show what would be executed without running
-
-**Example:**
-```bash
-drt investigate -a analysis/output_20251209_184032/ -c config.yaml
-drt investigate -a analysis/output_20251209_184032/ -c config.yaml -o ./my_reports
-```
-
-**What it does:**
-- Discovers all `*_investigate.sql` files in the analysis directory
-- Parses SQL files (handles markdown, multiple queries per file)
-- Executes queries on both baseline and target databases
-- Handles errors gracefully (continues on failures)
-- Generates HTML and CSV reports with side-by-side comparisons
-
 ## ⚙️ Configuration
 
 ### Database Connections
@@ -217,7 +187,7 @@ tables:
 ```yaml
 reporting:
   output_dir: "./reports"
-  investigation_dir: "./investigation_reports"
+
 
 logging:
   output_dir: "./logs"
@@ -249,7 +219,7 @@ Reports are saved to `./reports/` with timestamps.
 - **HTML Report** - Interactive report with collapsible query results, side-by-side baseline vs target comparison
 - **CSV Report** - Flattened structure with one row per query execution
 
-Investigation reports are saved to `./investigation_reports/` with timestamps.
+
 
 ## 🔄 Exit Codes
 
@@ -324,14 +294,14 @@ grep -i "FAIL\|ERROR" logs/drt_*.log
 ```
 src/drt/
 ├── cli/              # Command-line interface
-│   └── commands/     # CLI commands (compare, discover, validate, investigate)
+│   └── commands/     # CLI commands (compare, discover, validate)
 ├── config/           # Configuration management
 ├── database/         # Database connectivity (READ ONLY)
 ├── models/           # Data models
 ├── reporting/        # Report generators
 ├── services/         # Business logic
 │   ├── checkers/     # Comparison checkers
-│   ├── investigation.py  # Investigation service
+
 │   └── sql_parser.py     # SQL file parser
 └── utils/            # Utilities
 ```