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/kernel/P5-context-mod-sched.patch

@@ -0,0 +1,13 @@
+diff --git a/src/context/mod.rs b/src/context/mod.rs
+index 37c73f5..4f5d60f 100644
+--- a/src/context/mod.rs
++++ b/src/context/mod.rs
+@@ -22,7 +22,7 @@ use crate::{
+ 
+ use self::context::Kstack;
+ pub use self::{
+-    context::{BorrowedHtBuf, Context, Status},
++    context::{BorrowedHtBuf, Context, SchedPolicy, Status},
+     switch::switch,
+ };
+