feat: persistent DB host config, async DB ops, Exit button, test connection

- Save/load DB host from config.json (works both in dev and built .exe)
- All DB operations moved to background threads to prevent UI blocking
- Connection timeout set to 5s to avoid long hangs on unreachable host
- Added Test Connection button to Settings popup
- Added red Exit button fixed to bottom-right corner of main screen
- Updated DatabaseApp.spec with full Kivy deps (sdl2, glew, angle) and hidden imports
- PyInstaller-aware base path using sys.frozen for config.json persistence

database_manager.py

@@ -1,6 +1,18 @@
 import mysql.connector
 from mysql.connector import Error
 from typing import List, Tuple, Optional
+import json
+import os
+import sys
+
+# When frozen by PyInstaller, __file__ points to a temp folder that is deleted on exit.
+# sys.executable points to the .exe location, which is persistent.
+if getattr(sys, 'frozen', False):
+    _BASE_DIR = os.path.dirname(sys.executable)
+else:
+    _BASE_DIR = os.path.dirname(os.path.abspath(__file__))
+
+CONFIG_FILE = os.path.join(_BASE_DIR, 'config.json')
 
 class DatabaseManager:
     """
@@ -9,12 +21,53 @@ class DatabaseManager:
     """
     
     def __init__(self):
-        self.host = "localhost"
+        self.host = self._load_host()
         self.database = "cantare_injectie"
         self.user = "omron"
         self.password = "Initial01!"
         self.connection = None
-        self.init_database()
+        # init_database() is called asynchronously from the UI layer to avoid blocking
+
+    def _load_host(self) -> str:
+        """Load the database host from the config file, falling back to localhost."""
+        try:
+            if os.path.exists(CONFIG_FILE):
+                with open(CONFIG_FILE, 'r') as f:
+                    data = json.load(f)
+                    return data.get('host', 'localhost')
+        except Exception as e:
+            print(f"Could not read config file: {e}")
+        return 'localhost'
+
+    def save_host(self, host: str):
+        """Persist the database host to the config file."""
+        try:
+            data = {}
+            if os.path.exists(CONFIG_FILE):
+                with open(CONFIG_FILE, 'r') as f:
+                    data = json.load(f)
+            data['host'] = host
+            with open(CONFIG_FILE, 'w') as f:
+                json.dump(data, f, indent=2)
+        except Exception as e:
+            print(f"Could not save config file: {e}")
+
+    def test_connection(self, host: str) -> tuple:
+        """Test connectivity to the database using the given host. Returns (success: bool, message: str)."""
+        try:
+            test_conn = mysql.connector.connect(
+                host=host,
+                database=self.database,
+                user=self.user,
+                password=self.password,
+                connection_timeout=5
+            )
+            if test_conn.is_connected():
+                test_conn.close()
+                return True, f"Connected successfully to '{host}'"
+        except Error as e:
+            return False, str(e)
+        return False, "Connection failed"
     
     def get_connection(self):
         """Get a database connection."""
@@ -24,7 +77,8 @@ class DatabaseManager:
                     host=self.host,
                     database=self.database,
                     user=self.user,
-                    password=self.password
+                    password=self.password,
+                    connection_timeout=5
                 )
             return self.connection
         except Error as e: