Fix Vue property conflicts in PlatformServiceMixin implementation

- Remove duplicate property declarations from TopMessage component
- Use (this as any) type assertion for mixin methods
- Resolves 'Data property already defined' warnings
- Fixes 'this.dbQuery is not a function' runtime errors

src/utils/PlatformServiceMixin.ts

@@ -0,0 +1,136 @@
+/**
+ * Platform Service Mixin for Vue Components
+ *
+ * Provides class-level caching of platform service instances to avoid
+ * repeated PlatformServiceFactory.getInstance() calls throughout components.
+ *
+ * This mixin implements a hybrid approach combining:
+ * - Class-level service caching for performance
+ * - Vue composition API patterns for modern development
+ * - Mixin pattern for easy integration with existing class components
+ *
+ * Benefits:
+ * - Eliminates repeated PlatformServiceFactory.getInstance() calls
+ * - Provides consistent service access pattern across components
+ * - Improves performance with cached instances
+ * - Maintains type safety with TypeScript
+ *
+ * @author Matthew Raymer
+ * @version 1.0.0
+ * @since 2025-07-02
+ */
+
+import { PlatformServiceFactory } from "@/services/PlatformServiceFactory";
+import type { PlatformService } from "@/services/PlatformService";
+
+/**
+ * Mixin that provides cached platform service access to Vue components
+ *
+ * Usage:
+ * ```typescript
+ * @Component({
+ *   mixins: [PlatformServiceMixin]
+ * })
+ * export default class MyComponent extends Vue {
+ *   async someMethod() {
+ *     // Access cached platform service directly
+ *     const result = await this.platformService.dbQuery('SELECT * FROM users');
+ *   }
+ * }
+ * ```
+ */
+export const PlatformServiceMixin = {
+  data() {
+    return {
+      _platformService: null as PlatformService | null,
+    };
+  },
+
+  computed: {
+    /**
+     * Get the cached platform service instance
+     * Creates and caches the instance on first access
+     */
+    platformService(): PlatformService {
+      if (!(this as any)._platformService) {
+        (this as any)._platformService = PlatformServiceFactory.getInstance();
+      }
+      return (this as any)._platformService;
+    },
+
+    /**
+     * Check if running on Capacitor platform
+     */
+    isCapacitor(): boolean {
+      const service = (this as any).platformService as any;
+      return typeof service.isCapacitor === "function"
+        ? service.isCapacitor()
+        : false;
+    },
+
+    /**
+     * Check if running on web platform
+     */
+    isWeb(): boolean {
+      const service = (this as any).platformService as any;
+      return typeof service.isWeb === "function" ? service.isWeb() : false;
+    },
+
+    /**
+     * Check if running on Electron platform
+     */
+    isElectron(): boolean {
+      const service = (this as any).platformService as any;
+      return typeof service.isElectron === "function"
+        ? service.isElectron()
+        : false;
+    },
+
+    /**
+     * Get platform capabilities
+     */
+    capabilities() {
+      return (this as any).platformService.getCapabilities();
+    },
+  },
+
+  methods: {
+    /**
+     * Convenient database query method
+     * Shorthand for this.platformService.dbQuery()
+     */
+    async dbQuery(sql: string, params?: unknown[]) {
+      return await (this as any).platformService.dbQuery(sql, params);
+    },
+
+    /**
+     * Convenient database execution method
+     * Shorthand for this.platformService.dbExec()
+     */
+    async dbExec(sql: string, params?: unknown[]) {
+      return await (this as any).platformService.dbExec(sql, params);
+    },
+
+    /**
+     * Convenient database single row method
+     * Shorthand for this.platformService.dbGetOneRow()
+     */
+    async dbGetOneRow(sql: string, params?: unknown[]) {
+      return await (this as any).platformService.dbGetOneRow(sql, params);
+    },
+  },
+};
+
+/**
+ * Type-only export for components that need to declare the mixin interface
+ */
+export interface IPlatformServiceMixin {
+  platformService: PlatformService;
+  dbQuery(sql: string, params?: unknown[]): Promise<any>;
+  dbExec(sql: string, params?: unknown[]): Promise<any>;
+  dbGetOneRow(sql: string, params?: unknown[]): Promise<any>;
+  isCapacitor: boolean;
+  isWeb: boolean;
+  isElectron: boolean;
+  capabilities: any;
+}