Implement PlaceholderHelp component across various forms for enhanced user guidance

- Integrated PlaceholderHelp component into multiple forms including WelcomeForm, TagsManager, and StatsForm to provide contextual hints for available placeholders.
- Updated DiscordEmbedBuilder to support placeholder presets, improving user experience when creating embeds.
- Enhanced localization files to include new placeholder descriptions, ensuring clarity in both English and German.
- Refactored related components to maintain consistency in placeholder handling across the application.

packages/shared/src/phase2.ts

@@ -162,14 +162,23 @@ export const WELCOME_PLACEHOLDERS = [
   '{memberCount}'
 ] as const;
 
+/**
+ * Expands dashboard-friendly channel mentions `["123…"]` into Discord's
+ * native `<#123…>` mention format. Raw `<#id>` mentions are left untouched.
+ */
+export function expandBracketChannelMentions(template: string): string {
+  return template.replace(/\["(\d{17,20})"\]/g, '<#$1>');
+}
+
 export function applyWelcomePlaceholders(
   template: string,
   vars: Record<string, string | number>
 ): string {
-  return Object.entries(vars).reduce(
+  const withVars = Object.entries(vars).reduce(
     (acc, [name, value]) => acc.replaceAll(`{${name}}`, String(value)),
     template
   );
+  return expandBracketChannelMentions(withVars);
 }
 
 export function countEmojis(content: string): number {