refactor(import): remove non-functional DOCX/PDF/Confluence import stubs

These import paths relied on the private EE module that was deleted from
the repo. In the community build they either threw 'enterprise license'
(DOCX/PDF) or silently no-op'd (Confluence). The frontend buttons were
already removed in 38064064; this cleans up the dead backend stubs.

- import.service.ts: drop processDocx/processPdf methods, their dispatcher
  branches, the pageId computation + insertPage spread, and the now-unused
  moduleRef param/ModuleRef import
- file-import-task.service.ts: drop the Confluence branch and the now-unused
  moduleRef param/ModuleRef import
- import.controller.ts: restrict file extensions to .md/.html and zip
  sources to generic/notion; update the error message accordingly
- file.utils.ts: remove Confluence from the FileImportSource enum
- features.ts: remove the unused CONFLUENCE_IMPORT/DOCX_IMPORT/PDF_IMPORT
  feature keys

The isConfluenceImport logic in import-attachment.service.ts is intentionally
left in place (real shared attachment-parsing code, not a stub); its removal
is a separate, riskier refactor.

apps/server/src/integrations/import/import.controller.ts

@@ -51,7 +51,7 @@ export class ImportController {
     @AuthUser() user: User,
     @AuthWorkspace() workspace: Workspace,
   ) {
-    const validFileExtensions = ['.md', '.html', '.docx', '.pdf'];
+    const validFileExtensions = ['.md', '.html'];
 
     const maxFileSize = bytes('30mb');
 
@@ -101,8 +101,6 @@ export class ImportController {
     const sourceMap: Record<string, string> = {
       '.md': 'markdown',
       '.html': 'html',
-      '.docx': 'docx',
-      '.pdf': 'pdf',
     };
 
     if (createdPage) {
@@ -161,10 +159,10 @@ export class ImportController {
     const spaceId = file.fields?.spaceId?.value;
     const source = file.fields?.source?.value;
 
-    const validZipSources = ['generic', 'notion', 'confluence'];
+    const validZipSources = ['generic', 'notion'];
     if (!validZipSources.includes(source)) {
       throw new BadRequestException(
-        'Invalid import source. Import source must either be generic, notion or confluence.',
+        'Invalid import source. Import source must either be generic or notion.',
       );
     }