fix(scheduler): close post-failover rejoin detection gap (bug-1760)

An idle scheduler (nothing queued to publish) never noticed a dead
controller connection: sched_needs_rejoin was only ever set as a side
effect of an active client-library call, and an idle round makes none.
After any controller failover with nothing already in flight, jobs
submitted to the new primary stayed PEND indefinitely.

Adds xcecli_is_connection_broken() (libxce) -- a pure, socket-free read
of the transport's already-async-maintained dead/alive flag, set for
free by the existing RDHUP disconnect handler with zero application
calls. sched_check_pending_rejoin() now retries xcecli_join() on either
the existing reactive flag or this new passive signal, so a healthy
idle scheduler still makes zero extra network calls while a genuinely
dead connection self-heals within one ~1s round -- live-verified
against a 3-node HA cluster (rejoin fired ~300ms after new-primary
election with nothing submitted in between).

Also closes out bug-1735 (job memory/CPU usage reporting): confirmed
already fixed on this branch since 2026-08-30, just never marked in
the bug log.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XYdtrEWWZfKRRGED7raEYg

src/scheduler/testsuite/meson.build

@@ -1313,11 +1313,15 @@ sched_scheduler_decision_publish_retry_test = executable(
     scheduler_decision_publish_retry_test_srcs,
     include_directories:[incdir],
     dependencies: [scheduler_deps, unity_dep],
+    c_args: ['-DXCE_MAIN_C_PATH="'
+             + (meson.current_source_dir() / '..' / 'src' / 'main.c')
+             + '"'],
     link_args: ['-Wl,--wrap=xcecli_jobdispatch',
                '-Wl,--wrap=xcecli_set_pend_reason',
                '-Wl,--wrap=xcecli_join',
                '-Wl,--wrap=xcecli_start',
-               '-Wl,--wrap=xcecli_set_reconnect_handler'],
+               '-Wl,--wrap=xcecli_set_reconnect_handler',
+               '-Wl,--wrap=xcecli_is_connection_broken'],
     install: false)
 
 # Worst-case decision/allocation backpressure test (component-failover-