feat: Rebuild complete CSV import system for legacy data migration

PROBLEM SOLVED:
- Completely removed broken import functionality
- Built new robust, modular CSV import system from scratch
- Provides reliable data migration path for legacy .sc files

NEW IMPORT SYSTEM FEATURES:
✅ Modular CSV parsers for all 5 tables (ROLODEX, PHONE, FILES, LEDGER, QDROS)
✅ RESTful API endpoints with background processing (/api/admin/import/*)
✅ Admin web interface at /admin/import for file uploads
✅ Comprehensive validation and error handling
✅ Real-time progress tracking and status monitoring
✅ Detailed logging with import session tracking
✅ Transaction rollback on failures
✅ Batch import with dependency ordering
✅ Foreign key validation and duplicate detection

TECHNICAL IMPLEMENTATION:
- Clean /app/import_export/ module structure with base classes
- Enhanced logging system with import-specific logs
- Background task processing with FastAPI BackgroundTasks
- Auto-detection of CSV delimiters and encoding
- Field validation with proper data type conversion
- Admin authentication integration
- Console logging for debugging support

IMPORT WORKFLOW:
1. Admin selects table type and uploads CSV file
2. System validates headers and data structure
3. Background processing with real-time status updates
4. Detailed error reporting and success metrics
5. Import logs stored in logs/imports/ directory

SUPPORTED TABLES:
- ROLODEX (contacts/people) - 19 fields, requires: id, last
- PHONE (phone numbers) - 3 fields, requires: rolodex_id, phone
- FILES (case files) - 29 fields, requires: file_no, id, empl_num, file_type, opened, status, rate_per_hour
- LEDGER (transactions) - 12 fields, requires: file_no, date, t_code, t_type, empl_num, amount
- QDROS (documents) - 31 fields, requires: file_no

REMOVED FILES:
- app/api/unified_import_api.py
- app/services/unified_import.py
- app/api/flexible.py
- app/models/flexible.py
- templates/unified_import.html
- templates/flexible.html
- static/js/flexible.js
- All legacy import routes and references

TESTING COMPLETED:
✅ Schema validation for all table types
✅ CSV header validation
✅ Single file import functionality
✅ Multi-table dependency validation
✅ Error handling and logging
✅ API endpoint integration

READY FOR PRODUCTION: System tested and validated with sample data.
Administrators can now reliably import CSV files converted from legacy .sc files.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

app/main.py

@@ -175,6 +175,7 @@ from app.api.document_workflows import router as document_workflows_router
 from app.api.session_management import router as session_management_router
 from app.api.advanced_templates import router as advanced_templates_router
 from app.api.jobs import router as jobs_router
+from app.api.import_csv import router as import_csv_router
 
 logger.info("Including API routers")
 app.include_router(advanced_variables_router, prefix="/api/variables", tags=["advanced-variables"])
@@ -201,6 +202,7 @@ app.include_router(deadlines_router, prefix="/api/deadlines", tags=["deadlines"]
 app.include_router(document_workflows_router, prefix="/api/workflows", tags=["document-workflows"])
 app.include_router(labels_router, prefix="/api/labels", tags=["labels"])
 app.include_router(jobs_router, prefix="/api/jobs", tags=["jobs"])
+app.include_router(import_csv_router, prefix="/api/admin/import", tags=["import"])
 
 
 @app.get("/", response_class=HTMLResponse)
@@ -284,6 +286,15 @@ async def admin_page(request: Request):
     )
 
 
+@app.get("/admin/import", response_class=HTMLResponse)
+async def admin_import_page(request: Request):
+    """CSV Import page (admin only)"""
+    return templates.TemplateResponse(
+        "admin_import.html",
+        {"request": request, "title": "CSV Import - " + settings.app_name}
+    )
+
+