refactor: split monolithic app.py into modular Flask application with factory pattern

- Created app/ package with 6 modules:
  - __init__.py: Application factory (create_app function)
  - routes.py: All route handlers (473 lines)
  - models.py: Data persistence layer (41 lines)
  - validators.py: Input validation functions (48 lines)
  - email_service.py: Email sending functions (85 lines)
  - utils.py: Utility functions (30 lines)

- Implemented Flask application factory pattern
- Created run.py as minimal entry point
- Updated all test imports to use new module structure
- Fixed template/static folder paths for package structure

- All 102 tests passing
- Improved maintainability with clear separation of concerns
- Follows Flask best practices for scalable applications

app/utils.py

@@ -0,0 +1,30 @@
+"""
+Utility functions for the Flask job application system.
+"""
+from datetime import datetime
+from flask import session, current_app
+
+
+def check_rate_limit():
+    """
+    Check if user is submitting forms too quickly.
+    Returns (allowed: bool, wait_seconds: int)
+    """
+    now = datetime.now()
+    last_submit_str = session.get('last_submission_time')
+
+    if last_submit_str:
+        try:
+            last_submit = datetime.fromisoformat(last_submit_str)
+            elapsed = (now - last_submit).total_seconds()
+
+            if elapsed < current_app.config['RATE_LIMIT_SECONDS']:
+                wait_seconds = int(current_app.config['RATE_LIMIT_SECONDS'] - elapsed) + 1
+                return False, wait_seconds
+        except (ValueError, TypeError):
+            # Invalid timestamp, allow submission
+            pass
+
+    # Update last submission time
+    session['last_submission_time'] = now.isoformat()
+    return True, 0