feat: P0-P6 kernel scheduler + relibc threading comprehensive implementation

P0-P2: Barrier SMP, sigmask/pthread_kill races, robust mutexes, RT scheduling, POSIX sched API
P3: PerCpuSched struct, per-CPU wiring, work stealing, load balancing, initial placement
P4: 64-shard futex table, REQUEUE, PI futexes (LOCK_PI/UNLOCK_PI/TRYLOCK_PI), robust futexes, vruntime tracking, min-vruntime SCHED_OTHER selection
P5: setpriority/getpriority, pthread_setaffinity_np, pthread_setname_np, pthread_setschedparam (Redox)
P6: Cache-affine scheduling (last_cpu + vruntime bonus), NUMA topology kernel hints + numad userspace daemon

Stability fixes: make_consistent stores 0 (dead TID fix), cond.rs error propagation, SPIN_COUNT adaptive spinning, Sys::open &str fix, PI futex CAS race, proc.rs lock ordering, barrier destroy

Patches: 33 kernel + 58 relibc patches, all tracked in recipes
Docs: KERNEL-SCHEDULER-MULTITHREAD-IMPROVEMENT-PLAN.md updated, SCHEDULER-REVIEW-FINAL.md created
Architecture: NUMA topology parsing stays userspace (numad daemon), kernel stores lightweight NumaTopology hints

local/patches/base/P1-xhcid-uevent-logging.patch

@@ -0,0 +1,20 @@
+diff --git a/drivers/usb/xhcid/src/xhci/mod.rs b/drivers/usb/xhcid/src/xhci/mod.rs
+index f1c6d08e..a3f2e15c 100644
+--- a/drivers/usb/xhcid/src/xhci/mod.rs
++++ b/drivers/usb/xhcid/src/xhci/mod.rs
+@@ -904,6 +904,7 @@ impl<const N: usize> Xhci<N> {
+             match self.spawn_drivers(port_id) {
+                 Ok(()) => {
+                     info!("xhcid: uevent add device usb/{}", port_id.root_hub_port_num());
++                    // NOTE: driver-manager hotplug loop detects new USB devices via this log
+                 }
+                 Err(err) => {
+                     error!("Failed to spawn driver for port {}: `{}`", port_id, err)
+@@ -974,6 +975,8 @@ impl<const N: usize> Xhci<N> {
+             info!("xhcid: uevent remove device usb/{}", port_id.root_hub_port_num());
+             result
+         } else {
++            // NOTE: driver-manager hotplug loop detects USB device removal via this log
+             debug!(
+                 "Attempted to detach from port {}, which wasn't previously attached.",
+                 port_id