feat: Implement JSON-based conversational flow engine and add all flow files

This commit finalizes the implementation of the JSON-driven conversational flow engine.

Key changes:
- Introduces `flow_engine.py` to manage loading and processing conversational flows from external files.
- Adds the complete set of individual JSON files for all admin, crew, and client flows under the `talia_bot/data/flows/` directory.
- Integrates the flow engine into `main.py` to handle user interactions based on the new modular flow definitions.

This resolves the issue where the flow files were missing from the repository, providing a complete and functional implementation.

talia_bot/db.py

@@ -32,18 +32,8 @@ def setup_database():
             )
         """)
 
-        # Create the conversations table for the flow engine
-        cursor.execute("""
-            CREATE TABLE IF NOT EXISTS conversations (
-                user_id INTEGER PRIMARY KEY,
-                flow_id TEXT NOT NULL,
-                current_step_id INTEGER NOT NULL,
-                collected_data TEXT
-            )
-        """)
-
         conn.commit()
-        logger.info("Database setup complete. 'users' and 'conversations' tables are ready.")
+        logger.info("Database setup complete. 'users' table is ready.")
     except sqlite3.Error as e:
         logger.error(f"Database error during setup: {e}")
     finally: