lint: add explicit return types and drop redundant/unnecessary type constructs

- Add explicit `(): void` return types to several useEffect cleanup
  callbacks (settingTabComponent, ColorPicker, AdvancedToolbarSettings,
  mobileModifyComponent).
- Widen Mode's literal union with `(string & {})` instead of a bare
  string constituent, preserving autocomplete without the redundant
  type warning.
- Drop an unnecessary `as ItemView` cast in pageHeaderManager now that
  the preceding instanceof guard already narrows the type.
- Switch eslint.config.mts from the deprecated tseslint.config() to
  eslint's own defineConfig().

Type-level only, no runtime behavior change.

eslint.config.mts

@@ -1,9 +1,9 @@
 import tseslint from 'typescript-eslint';
 import obsidianmd from 'eslint-plugin-obsidianmd';
 import globals from 'globals';
-import { globalIgnores } from 'eslint/config';
+import { defineConfig, globalIgnores } from 'eslint/config';
 
-export default tseslint.config(
+export default defineConfig(
 	globalIgnores([
 		'node_modules',
 		'build',

src/manager/commands/pageHeaderManager.ts

@@ -26,7 +26,7 @@ export default class PageHeaderManager extends CommandManagerBase {
 		const buttons = this.buttonsFor(leaf, true);
 		if (!buttons || buttons.has(id)) return;
 
-		const buttonIcon = (view as ItemView).addAction(icon, name, () => {
+		const buttonIcon = view.addAction(icon, name, () => {
 			this.plugin.app.workspace.setActiveLeaf(leaf, { focus: true });
 			this.plugin.app.commands.executeCommandById(id);
 		});

src/types.ts

@@ -61,7 +61,7 @@ export interface Tab {
 	tab: h.JSX.Element;
 }
 
-export type Mode = "desktop" | "any" | "mobile" | string;
+export type Mode = "desktop" | "any" | "mobile" | (string & {});
 
 export interface CommandIconPair {
 	id: string;

src/ui/components/AdvancedToolbarSettings.tsx

@@ -221,7 +221,9 @@ export default function AdvancedToolbarSettings({
 		if (ref.current) {
 			render(ref.current, plugin);
 		}
-		return () => ref.current && ref.current.empty();
+		return (): void => {
+			ref.current && ref.current.empty();
+		};
 	}, []);
 
 	return (

src/ui/components/ColorPicker/ColorPicker.tsx

@@ -19,7 +19,9 @@ export const ColorPicker = ({
 				.onChange(onChange);
 		}
 
-		return () => ref.current?.empty?.();
+		return (): void => {
+			ref.current?.empty?.();
+		};
 	}, [onChange, initialColor]);
 
 	return <div ref={ref} className="cmdr-flex cmdr-items-center" />;

src/ui/components/mobileModifyComponent.tsx

@@ -18,7 +18,7 @@ export default function MobileModifyComponent({
 			this.forceUpdate();
 		};
 		addEventListener("cmdr-icon-changed", update);
-		return () => removeEventListener("cmdr-icon-changed", update);
+		return (): void => removeEventListener("cmdr-icon-changed", update);
 	}, []);
 
 	return (

src/ui/components/settingTabComponent.tsx

@@ -37,7 +37,7 @@ export default function settingTabComponent({
 
 	useEffect(() => {
 		addEventListener("keydown", tabToNextTab);
-		return () => removeEventListener("keydown", tabToNextTab);
+		return (): void => removeEventListener("keydown", tabToNextTab);
 	}, [activeTab]);
 
 	//This is used to remove the initial onclick event listener.
@@ -342,7 +342,7 @@ export function TabHeader({
 		}
 
 		el.addEventListener("wheel", handleScroll);
-		return () => el.removeEventListener("wheel", handleScroll);
+		return (): void => el.removeEventListener("wheel", handleScroll);
 	}, []);
 
 	useEffect(