feat(file-browser): Implement NavStack class for navigation history management

Abstract navigation tracking, history state management, and navbar UI syncing into a dedicated `EventTarget` class.

Create `NavStack` class (`src/pages/fileBrowser/NavStack.js`):
- Implement `NavStack` extending `EventTarget` with a custom `Symbol.toStringTag` property
- Add `push`, `pop`, `popUntil`, `get` (supporting negative indexing), `has`, `on`, `off`, and `toJSON` methods with parameter validation
- Maintain an internal `#urlSet` to prevent duplicate stack entries
- Queue microtasks for `update` event dispatching, providing read-only `added` and `removed` location diffs in event details

Integrate `NavStack` into file browser (`src/pages/fileBrowser/fileBrowser.js`):
- Replace manual `state` array and direct `localStorage` persistence with a `NavStack` instance
- Listen to `update` events on `NavStack` to persist state to `localStorage`, clean up removed navbar elements and `actionStack` entries, and register new back-navigation actions
- Cache navbar DOM elements using a `navBarEls` Map with `getOrInsertComputed`
- Refactor `navigate` to accept location objects or strings and manage stack state using `navStack.has`, `navStack.popUntil`, and `navStack.push`
- Refactor `loadStates` to push history entries into `navStack` and navigate directly to the top item (`navStack.get(-1)`)
- Update folder selection button state (`$openFolder.disabled`) in `render()` and remove obsolete `pushState()` helper function

(AI generated commit message)

Author: AuDevTist1C

src/pages/fileBrowser/NavStack.js

@@ -0,0 +1,135 @@
+import Url from "utils/Url";
+
+/**
+ * @typedef {{url: string, name: string}} Location
+ */
+
+export default class NavStack extends EventTarget {
+	static {
+		Object.defineProperty(this.prototype, Symbol.toStringTag, {
+			value: "NavStack",
+			configurable: true,
+		});
+	}
+
+	get length() {
+		return this.#arr.length;
+	}
+	toJSON() {
+		return this.#arr.map((obj) => ({ ...obj }));
+	}
+	on() {
+		return this.addEventListener(...arguments);
+	}
+	off() {
+		return this.removeEventListener(...arguments);
+	}
+
+	/** @type {null | { added: Map<string, string>, removed: Set<string> }} */
+	#updatedURLs;
+	#queueUpdateEvent() {
+		if (this.#updatedURLs) return;
+		const added = new Map();
+		const removed = new Set();
+		this.#updatedURLs = Object.freeze({ added, removed });
+		queueMicrotask(() => {
+			this.#updatedURLs = null;
+			this.dispatchEvent(
+				new CustomEvent("update", {
+					detail: Object.freeze({
+						get added() {
+							return added.entries();
+						},
+						get removed() {
+							return removed.values();
+						},
+					}),
+				}),
+			);
+		});
+	}
+
+	/** @type {Set<string>} */
+	#urlSet = new Set();
+	/** @type {Array<Location>} */
+	#arr = [];
+	/**
+	 * @param {{ url: string, name?: string } | string} url
+	 * @param {string} [name]
+	 */
+	push(url, name) {
+		if (typeof url === "object") ({ url, name } = url);
+		if (!(url = `${url ?? ""}`)) {
+			throw new TypeError(
+				"NavStack.prototype.push(" +
+					"url: { url: string, name?: string } | string, name?: string): \n" +
+					'"url" is either missing, null or undefined, or resolves to an empty string.',
+			);
+		}
+		const urlSet = this.#urlSet;
+		if (urlSet.has(url)) return;
+		urlSet.add(url);
+		name = `${name ?? ""}` || Url.basename(url) || url;
+		const arr = this.#arr;
+		const i = arr.length;
+		arr[i] = { url, name };
+
+		this.#queueUpdateEvent();
+		const { added, removed } = this.#updatedURLs;
+		if (removed.has(url)) removed.delete(url);
+		else added.set(url, { name, index: i });
+	}
+	/**
+	 * @param {string} [url]
+	 */
+	#popUntil(url) {
+		const urlSet = this.#urlSet;
+		const arr = this.#arr;
+		for (let i = arr.length - 1; i >= 0; i--) {
+			const item = arr[i];
+			const url2 = item.url;
+			if (url && url === url2) return;
+			this.#urlSet.delete(url2);
+			arr.length = i;
+
+			this.#queueUpdateEvent();
+			const { added, removed } = this.#updatedURLs;
+			if (!added.has(url2)) removed.add(url2);
+			else added.delete(url2);
+
+			if (!url) return;
+		}
+	}
+	/**
+	 * @param {string} url
+	 */
+	popUntil(url) {
+		if ((url = `${url ?? ""}`)) return this.#popUntil(url);
+		throw new TypeError(
+			"NavStack.prototype.popUntil(url: string): \n" +
+				'"url" is either missing, null or undefined, or resolves to an empty string.',
+		);
+	}
+	pop() {
+		return this.#popUntil();
+	}
+	/**
+	 * @param {number} i
+	 * @returns {Location}
+	 */
+	get(i) {
+		if ((i = +i) !== i) {
+			throw new TypeError(
+				'NavStack.prototype.get(i: number): "i" is either missing or resolves to NaN.',
+			);
+		}
+		const arr = this.#arr;
+		const l = arr.length;
+		if (i < 0) i += l;
+		if (i < 0 || i > l - 1) return;
+		return { ...arr[i] };
+	}
+	has(url) {
+		return this.#urlSet.has(`${url ?? ""}`);
+	}
+}