Platform review round 2: audit logging migration, nav unification, DB indexes, and UI polish

- Migrate ~41 inline audit log calls to shared logAudit() utility across all routers
- Add transaction-aware prisma parameter to logAudit() for atomic operations
- Unify jury/mentor/observer navigation into shared RoleNav component
- Add composite DB indexes (Evaluation, GracePeriod, AuditLog) for query performance
- Fix profile page: consolidate dual save buttons, proper useEffect initialization
- Enhance auth error page with MOPC branding and navigation
- Improve observer dashboard with prominent read-only badge
- Fix DI-3: fetch projects before bulk status update for accurate notifications
- Remove unused aiBoost field from smart-assignment scoring
- Add shared image-upload utility and structured logger module

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

src/lib/logger.ts

@@ -0,0 +1,59 @@
+/**
+ * Structured Logger Utility
+ *
+ * Provides tagged, level-aware logging for consistent output across the application.
+ * Respects LOG_LEVEL environment variable and NODE_ENV for default levels.
+ *
+ * Usage:
+ *   import { logger } from '@/lib/logger'
+ *   logger.info('AI Assignment', 'Processing batch', { batchSize: 15 })
+ *   logger.error('Storage', 'Upload failed', error)
+ */
+
+type LogLevel = 'debug' | 'info' | 'warn' | 'error'
+
+const LOG_LEVELS: Record<LogLevel, number> = {
+  debug: 0,
+  info: 1,
+  warn: 2,
+  error: 3,
+}
+
+function getConfiguredLevel(): LogLevel {
+  const envLevel = process.env.LOG_LEVEL?.toLowerCase()
+  if (envLevel && envLevel in LOG_LEVELS) {
+    return envLevel as LogLevel
+  }
+  return process.env.NODE_ENV === 'production' ? 'warn' : 'debug'
+}
+
+function shouldLog(level: LogLevel): boolean {
+  return LOG_LEVELS[level] >= LOG_LEVELS[getConfiguredLevel()]
+}
+
+function formatTimestamp(): string {
+  return new Date().toISOString()
+}
+
+export const logger = {
+  debug: (tag: string, message: string, data?: unknown): void => {
+    if (shouldLog('debug')) {
+      console.debug(`${formatTimestamp()} [DEBUG] [${tag}]`, message, data ?? '')
+    }
+  },
+  info: (tag: string, message: string, data?: unknown): void => {
+    if (shouldLog('info')) {
+      console.info(`${formatTimestamp()} [INFO] [${tag}]`, message, data ?? '')
+    }
+  },
+  warn: (tag: string, message: string, data?: unknown): void => {
+    if (shouldLog('warn')) {
+      console.warn(`${formatTimestamp()} [WARN] [${tag}]`, message, data ?? '')
+    }
+  },
+  error: (tag: string, message: string, data?: unknown): void => {
+    if (shouldLog('error')) {
+      console.error(`${formatTimestamp()} [ERROR] [${tag}]`, message, data ?? '')
+    }
+  },
+}