Fix invite link in Join Lobby (#1695)

Closes #1694 

## Description:

Currently when you paste the invitation (
[https://openfront.io#join=QwIr5aK4](https://openfront.io/#join=QwIr5aK4)
) it puts undefined in the input so I made this issue to make a PR and
fix the problem.

<img width="410" height="370" alt="image"
src="https://github.com/user-attachments/assets/d2cf4321-49e3-4e81-987e-66eff2e4d14c"
/>

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA agreement (only required once).

## Please put your Discord username so you can be contacted if a bug or
regression is found:

kipstzz

src/client/JoinPrivateLobbyModal.ts

@@ -135,14 +135,25 @@ export class JoinPrivateLobbyModal extends LitElement {
     );
   }
 
-  private setLobbyId(id: string) {
-    if (id.startsWith("http")) {
-      this.lobbyIdInput.value = id.split("join/")[1];
+  private extractLobbyIdFromUrl(input: string): string {
+    if (input.startsWith("http")) {
+      if (input.includes("#join=")) {
+        const params = new URLSearchParams(input.split("#")[1]);
+        return params.get("join") ?? input;
+      } else if (input.includes("join/")) {
+        return input.split("join/")[1];
+      } else {
+        return input;
+      }
     } else {
-      this.lobbyIdInput.value = id;
+      return input;
     }
   }
 
+  private setLobbyId(id: string) {
+    this.lobbyIdInput.value = this.extractLobbyIdFromUrl(id);
+  }
+
   private handleChange(e: Event) {
     const value = (e.target as HTMLInputElement).value.trim();
     this.setLobbyId(value);
@@ -151,15 +162,7 @@ export class JoinPrivateLobbyModal extends LitElement {
   private async pasteFromClipboard() {
     try {
       const clipText = await navigator.clipboard.readText();
-
-      let lobbyId: string;
-      if (clipText.startsWith("http")) {
-        lobbyId = clipText.split("join/")[1];
-      } else {
-        lobbyId = clipText;
-      }
-
-      this.lobbyIdInput.value = lobbyId;
+      this.setLobbyId(clipText);
     } catch (err) {
       console.error("Failed to read clipboard contents: ", err);
     }