test(host): make two host tests portable to Windows

The Windows host test suite hit two pre-existing portability failures
(the autonomous Windows bring-up never ran `cargo test` on the VM):

- `vdisplay::detect_active_session_*` asserted a non-empty XDG runtime
  dir — a Linux concept with no Windows equivalent. Gate just that
  assertion to Linux (keep the call so the fn stays used → no dead_code).
- `mgmt::openapi_document_is_complete_and_checked_in` did a byte compare
  against the checked-in spec, which git may check out CRLF on Windows
  while serde_json emits LF. Compare content with `\r` stripped.

Host suite now 73/73 on x86_64-pc-windows-msvc; Linux unchanged (78 ok).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/mgmt.rs

@@ -1588,9 +1588,11 @@ mod tests {
         );
 
         let checked_in = include_str!("../../../docs/api/openapi.json");
+        // Compare content, not line-ending style: the generated `json` is LF (serde_json), but git
+        // may check the file out CRLF on Windows.
         assert_eq!(
-            json.trim(),
-            checked_in.trim(),
+            json.trim().replace('\r', ""),
+            checked_in.trim().replace('\r', ""),
             "docs/api/openapi.json is stale — regenerate with: \
              cargo run -p punktfunk-host -- openapi > docs/api/openapi.json"
         );