test(skip): SSE routes for file browser not yet implemented

[curdriceaurora]

One test in tests/test_web_files_routes.py (test_files_sse_placeholder) is skipped because SSE routes for the file browser are not yet implemented. Related: #1027.

[curdriceaurora]

Closing — feature not yet implemented (Phase 3 / backlog). Tests correctly skipped until feature is built.