feat: SAS-R0 signature-feature attestation - not-ready means very-early panic

- SAS-E01: scheduler bootstrap failure was "non-fatal" -> panic (O(1)
  scheduler must stand up or nothing runs)
- PCKC-E01: boot-time key-derive roundtrip in utsm_init (get_or_derive
  probe segment, all-zero key or error -> panic; probe slot invalidated)
- DKM-E04..E07: manifest required-driver failures (module missing /
  ELF invalid / symbol scan fail / load fail) -> panic instead of
  "abort stage" silent continue
- QEMU verify: pckc derive roundtrip ok, sealed MAC established,
  selftest OK, boot reaches wizard, zero spurious panics

[STUB] P0/UTSM SAS-R0 attestation | 剩余STUB命中=101（违规=0） | “特色不是招牌，是性命” | 已提交=<this>

CODE/UTSM/kernel/main.c

@@ -378,7 +378,10 @@ void kernel_main(void) {
         log_hex64("[SCHED] cfg enable=", (u64)g_sched_enabled_cfg);
         log_hex64("[SCHED] cfg demo_ms=", s_demo_ms);
         if (utsm_sched_bootstrap_init() < 0) {
-            log_warn("[UTSM] scheduler bootstrap failed (non-fatal)");
+            /* SAS-R0 特色自证：调度器 bootstrap 失败 = 单地址空间 O(1)
+             * 调度器没有真正立起来，零降级 panic（SAS-E01） */
+            panic_full("SAS-E01 SCHED BOOTSTRAP FAILED",
+                       "SAS-R0-PCQ scheduler bootstrap failed (was: non-fatal)", 0);
         }
     }