chore: add GitHub Copilot agent, fix ESLint config, update task list

- .github/agents/ProcessTasks.agent.md: Copilot agent definition
- eslint.config.ts: minor lint rule adjustment
- Docs/Tasks.md: update completed and in-progress task status

frontend/eslint.config.ts

@@ -21,7 +21,7 @@ export default tseslint.config(
       ...reactHooks.configs.recommended.rules,
       "@typescript-eslint/no-explicit-any": "error",
       "@typescript-eslint/explicit-function-return-type": "warn",
-      "@typescript-eslint/no-unused-vars": ["error", { argsIgnorePattern: "^_" }],
+      "@typescript-eslint/no-unused-vars": ["error", { argsIgnorePattern: "^_", varsIgnorePattern: "^_" }],
     },
   },
   prettierConfig,