feat(xce-harness-component): promote ctrlstatus_fmt.h to shared xce/ include path

Move the one genuinely shared header (header-only, static inline, zero
link dependency) from src/controller/testsuite/ to src/include/xce/,
alongside the existing cross-daemon shared headers (cluster.h, types.h,
errnox.h). Repoint its three current consumers (harness's test.c and
joblist_display.c, controller's test_ctrlstatus.c) to the new path.
test_joblist_display.c is intentionally left on the old path -- it
relocates in task 2.2.

Also removes src/harness/meson.build's temporary '../controller/testsuite'
incdir shim, which task 1.1 added and explicitly marked for removal once
this task landed.

controller_unit_test: 1228 Tests 0 Failures 0 Ignored (unchanged from
task 1.1's baseline, confirming a header-path-only change).

Task 1.2 of xce-harness-component.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RLSNJhNoULvVcUhXEFafQC

src/controller/testsuite/test_ctrlstatus.c

@@ -22,7 +22,7 @@
 #include "persist.h"
 #include "xce/cluster_def.h"
 
-#include "ctrlstatus_fmt.h" /* ctrlstatus_format_time_ms (task 6.3) */
+#include "xce/ctrlstatus_fmt.h" /* ctrlstatus_format_time_ms (task 6.3) */
 
 /* ── helpers ────────────────────────────────────────────────── */