fix: add missing tier field to all AppMetadata, fix build errors

- Add tier: "" to all AppMetadata match arms (was missing from 30+ arms)
- Use std::thread::available_parallelism() instead of num_cpus crate
- Remove unused num_cpus dependency
- Fix unused variable warning in health_monitor.rs

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/monitoring/mod.rs

@@ -344,7 +344,9 @@ impl MetricsStore {
                 }
                 AlertRuleKind::CpuLoad => {
                     // Alert if 5-min load average exceeds threshold * core count
-                    let cores = num_cpus::get() as f64;
+                    let cores = std::thread::available_parallelism()
+                        .map(|n| n.get() as f64)
+                        .unwrap_or(4.0);
                     let max_load = rule.threshold * cores;
                     if snapshot.system.load_avg_5 > max_load {
                         new_alerts.push(FiredAlert {