v1.8.53: fix Redis and MariaDB GUI tabs — wrong client API calls

- redis_tab: fix RedisClient constructor (pass server dict, not alias+store)
- redis_tab: add connect() call, add disconnect on server switch
- redis_tab: remove non-existent db= parameter from execute(), use select_db()
- redis_client: add select_db() method for runtime DB switching
- query_tab: fix use_database() → switch_database(), close() → disconnect()
- query_tab: fix execute() → execute_query() with dict unpacking
- query_tab: add missing connect() call after SQLClient creation

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gui/tabs/redis_tab.py

@@ -105,6 +105,11 @@ class RedisTab(ctk.CTkFrame):
 
     def set_server(self, alias: str | None):
         """Called when user selects a server in sidebar."""
+        if self._client:
+            try:
+                self._client.disconnect()
+            except Exception:
+                pass
         self._current_alias = alias
         self._client = None
         self._command_history.clear()
@@ -143,7 +148,8 @@ class RedisTab(ctk.CTkFrame):
         def _do():
             try:
                 client = self._get_client()
-                result = client.execute(cmd, db=db)
+                client.select_db(db)
+                result = client.execute(cmd)
                 formatted = self._format_result(result)
                 self.after(0, lambda: self._append_output(formatted))
             except Exception as e:
@@ -162,7 +168,13 @@ class RedisTab(ctk.CTkFrame):
 
     def _get_client(self) -> RedisClient:
         if self._client is None:
-            self._client = RedisClient(self._current_alias, self.store)
+            server = self.store.get_server(self._current_alias)
+            if not server:
+                raise ConnectionError(f"Server '{self._current_alias}' not found")
+            self._client = RedisClient(server)
+            if not self._client.connect():
+                self._client = None
+                raise ConnectionError(f"Cannot connect to Redis '{self._current_alias}'")
         return self._client
 
     # ── Stats refresh ──
@@ -175,8 +187,9 @@ class RedisTab(ctk.CTkFrame):
             try:
                 client = self._get_client()
                 db = int(self._db_var.get())
-                keys_count = client.execute("DBSIZE", db=db)
-                info = client.execute("INFO memory", db=db)
+                client.select_db(db)
+                keys_count = client.execute("DBSIZE")
+                info = client.execute("INFO memory")
 
                 # Parse memory from INFO output
                 memory = "—"