Merge all role-dispatcher pages into single files; add FileBrowser with file-type icons

- DashboardPage, Projects, RequestsPage, ProjectDetailPage, RequestDetail: each now handles team/external/client in one file via role flags — removed 10 old role-specific sub-files
- Layout: client Company nav link goes directly to /company/:id when user has a single company
- FileBrowser: replace emoji icons with colored extension-text badges (square); folder icon stays 📁; Adobe/Figma/design-tool colors for design files
- CompaniesPage: merged team Companies + client company routing (single-company redirect, multi-company list)
- FileSharing: integrated FileBrowser component
- Removed: seafile API + lib, old ServerStatus, TaskDetail, role-split page files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

vercel.json

@@ -1,3 +1,6 @@
 {
-  "rewrites": [{ "source": "/((?!\\.well-known).*)", "destination": "/index.html" }]
+  "rewrites": [{ "source": "/((?!\\.well-known).*)", "destination": "/index.html" }],
+  "functions": {
+    "api/backfill-request-files.js": { "maxDuration": 300 }
+  }
 }