fix(models): remove duplicate schema indexes for clean startup

- GovernanceRule: Remove duplicate category index (uses compound index)
- VerificationLog: Remove duplicate verifiedAt index (uses compound + TTL)
- VariableValue: Remove duplicate category index (standalone index exists)

Eliminates 3 Mongoose duplicate index warnings on server startup
Server now starts with zero warnings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/models/GovernanceRule.model.js

@@ -74,7 +74,7 @@ const governanceRuleSchema = new mongoose.Schema({
     type: String,
     enum: ['content', 'security', 'privacy', 'technical', 'process', 'values', 'other'],
     default: 'other',
-    index: true,
+    // Note: Indexed via compound index { category: 1, active: 1 } below
     description: 'Category for filtering and organization'
   },
 

src/models/VariableValue.model.js

@@ -58,7 +58,7 @@ const variableValueSchema = new mongoose.Schema({
     type: String,
     enum: ['database', 'security', 'config', 'path', 'url', 'port', 'credential', 'feature_flag', 'other'],
     default: 'other',
-    index: true,
+    // Note: Indexed via standalone index { category: 1 } below
     description: 'Category for organizing variables'
   },
 

src/models/VerificationLog.model.js

@@ -201,7 +201,7 @@ const verificationLogSchema = new mongoose.Schema({
   verifiedAt: {
     type: Date,
     default: Date.now,
-    index: true,
+    // Note: Indexed via compound indexes and TTL index below
     description: 'When verification was performed'
   }