fix: resolve 17 P2 defects and 5 P3 defects from pre-launch audit

Batch fix covering multiple modules:
- P2-01: HandRegistry Semaphore-based max_concurrent enforcement
- P2-03: Populate toolCount/metricCount from Hand trait methods
- P2-06: heartbeat_update_config minimum interval validation
- P2-07: ReflectionResult used_fallback marker for rule-based fallback
- P2-08/09: identity_propose_change parameter naming consistency
- P2-10: ClassroomMetadata is_placeholder flag for LLM failure
- P2-11: classroomStore userDidCloseDuringGeneration intent tracking
- P2-12: workflowStore pipeline_create sends actionType
- P2-13/14: PipelineInfo step_count + PipelineStepInfo for proper step mapping
- P2-15: Pipe transform support in context.resolve (8 transforms)
- P2-16: Mustache {{...}} → \${...} auto-normalization
- P2-17: SaaSLogin password placeholder 6→8
- P2-19: serialize_skill_md + update_skill preserve tools field
- P2-22: ToolOutputGuard sensitive patterns from warn→block
- P2-23: Mutex::unwrap() → unwrap_or_else in relay/service.rs
- P3-01/03/07/08/09: Various P3 fixes
- DEFECT_LIST.md: comprehensive status sync (43/51 fixed, 8 remaining)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktop/src-tauri/src/intelligence/heartbeat.rs

@@ -715,6 +715,17 @@ pub async fn heartbeat_init(
     config: Option<HeartbeatConfig>,
     state: tauri::State<'_, HeartbeatEngineState>,
 ) -> Result<(), String> {
+    // P2-06: Validate minimum interval (prevent busy-loop)
+    const MIN_INTERVAL_MINUTES: u64 = 1;
+    if let Some(ref cfg) = config {
+        if cfg.interval_minutes < MIN_INTERVAL_MINUTES {
+            return Err(format!(
+                "interval_minutes must be >= {} (got {})",
+                MIN_INTERVAL_MINUTES, cfg.interval_minutes
+            ));
+        }
+    }
+
     let engine = HeartbeatEngine::new(agent_id.clone(), config);
 
     // Restore last interaction time from VikingStorage metadata
@@ -822,6 +833,14 @@ pub async fn heartbeat_update_config(
     config: HeartbeatConfig,
     state: tauri::State<'_, HeartbeatEngineState>,
 ) -> Result<(), String> {
+    // P2-06: Validate minimum interval (same as heartbeat_init)
+    const MIN_INTERVAL_MINUTES: u64 = 1;
+    if config.interval_minutes < MIN_INTERVAL_MINUTES {
+        return Err(format!(
+            "interval_minutes must be >= {} (got {})",
+            MIN_INTERVAL_MINUTES, config.interval_minutes
+        ));
+    }
     let engines = state.lock().await;
     let engine = engines
         .get(&agent_id)