feat(office): add Workspace TUI with shared bootstrap and test suite

Introduce the office Bubble Tea browser (module tree, multi-select lists,
markdown preview) alongside oo, with cmd/internal/bootstrap for shared auth,
unit tests across preview/model/ui/fetch, CI build for both binaries, and
GoReleaser archives for office.

Co-authored-by: Cursor <cursoragent@cursor.com>

.env.example

@@ -21,3 +21,7 @@ ONLYOFFICE_CALENDAR_ID=1
 ONLYOFFICE_PROJECT_ID=33
 
 # oo mails uses ONLYOFFICE_URL/USER/PASS above (Workspace Mail addon).
+
+# cmd/office TUI — optional Document Server for DOCX→HTML preview:
+# ONLYOFFICE_DOCS_URL=https://docs.example.com
+# ONLYOFFICE_DOCS_SECRET=