feat: Implement JSON-based conversational flow engine

This commit introduces a new `FlowEngine` to manage conversational flows based on JSON definitions.

Key changes:
- Created `talia_bot/modules/flow_engine.py` to handle the logic of parsing and executing flows.
- Added a `conversations` table to the database to persist user state during flows.
- Created the `talia_bot/data/flows` directory and added a sample `create_project.json` flow.
- Integrated the `FlowEngine` into `main.py` with a `universal_handler` that routes user input to the engine or to legacy handlers.

talia_bot/db.py

@@ -32,8 +32,18 @@ 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' table is ready.")
+        logger.info("Database setup complete. 'users' and 'conversations' tables are ready.")
     except sqlite3.Error as e:
         logger.error(f"Database error during setup: {e}")
     finally: