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/components/SaaS/SaaSLogin.tsx

@@ -55,8 +55,8 @@ export function SaaSLogin({ onLogin, onLoginWithTotp, onRegister, initialUrl, is
         setLocalError('邮箱格式不正确');
         return;
       }
-      if (password.length < 6) {
-        setLocalError('密码长度至少 6 个字符');
+      if (password.length < 8) {
+        setLocalError('密码长度至少 8 个字符');
         return;
       }
       if (password !== confirmPassword) {
@@ -322,7 +322,7 @@ export function SaaSLogin({ onLogin, onLoginWithTotp, onRegister, initialUrl, is
                   type={showPassword ? 'text' : 'password'}
                   value={password}
                   onChange={(e) => setPassword(e.target.value)}
-                  placeholder={isRegister ? '至少 6 个字符' : 'Enter password'}
+                  placeholder={isRegister ? '至少 8 个字符' : 'Enter password'}
                   autoComplete={isRegister ? 'new-password' : 'current-password'}
                   className="w-full px-3 pr-10 py-2 border border-gray-300 rounded-lg text-sm focus:outline-none focus:ring-2 focus:ring-emerald-500/20 focus:border-emerald-500 bg-white text-gray-900"
                   disabled={isLoggingIn}