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.test.ts

@@ -17,6 +17,16 @@ describe('phase2 helpers', () => {
     expect(result).toBe('Hello <@1> on Nexumi');
   });
 
+  it('expands bracket channel mentions', () => {
+    const result = applyWelcomePlaceholders('Join ["123456789012345678"] please', {});
+    expect(result).toBe('Join <#123456789012345678> please');
+  });
+
+  it('keeps native discord channel mentions', () => {
+    const result = applyWelcomePlaceholders('Join <#123456789012345678> please', {});
+    expect(result).toBe('Join <#123456789012345678> please');
+  });
+
   it('detects discord invites', () => {
     expect(isDiscordInvite('join https://discord.gg/test')).toBe(true);
     expect(isDiscordInvite('hello world')).toBe(false);