Phase 2: Performance Profiling Setup - Add profiling utilities

- Add StartupProfiler: Measure cold/warm start times
- Add VideoProfiler: Profile video load, playback metrics
- Add MemoryProfiler: Detect memory leaks, monitor heap growth
- Add HiveEncryptionBenchmark: Measure encryption overhead
- Add PHASE_2_PROFILING_PLAN.md: Complete testing procedures

Ready for profiling execution once Flutter SDK is initialized

lib/core/utils/startup_profiler.dart

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+import 'dart:async';
+import 'package:flutter/foundation.dart';
+
+/// Profiler for startup time measurements
+class StartupProfiler {
+  static final _timings = <String, Stopwatch>{};
+  static final _marks = <String, DateTime>{};
+
+  /// Start timing a phase
+  static void start(String label) {
+    _timings[label] = Stopwatch()..start();
+    _marks[label] = DateTime.now();
+    if (kDebugMode) {
+      print('⏱️  START: $label (${DateTime.now().toIso8601String()})');
+    }
+  }
+
+  /// Mark completion of a phase
+  static void mark(String label) {
+    final watch = _timings[label];
+    if (watch != null) {
+      watch.stop();
+      final ms = watch.elapsedMilliseconds;
+      if (kDebugMode) {
+        print('✅ $label: ${ms}ms');
+      }
+    }
+  }
+
+  /// Get elapsed time for a label
+  static int? getElapsedMs(String label) {
+    return _timings[label]?.elapsedMilliseconds;
+  }
+
+  /// Report all metrics
+  static Future<void> reportAll() async {
+    if (kDebugMode) {
+      print('\n' + ('=' * 50));
+      print('⏱️  STARTUP METRICS');
+      print('=' * 50);
+      _timings.forEach((key, watch) {
+        print('  $key: ${watch.elapsedMilliseconds}ms');
+      });
+      print('=' * 50 + '\n');
+    }
+  }
+
+  /// Export metrics as JSON for logging
+  static Map<String, int> toJson() {
+    return _timings
+        .map((key, watch) => MapEntry(key, watch.elapsedMilliseconds));
+  }
+
+  /// Reset all timings
+  static void reset() {
+    _timings.clear();
+    _marks.clear();
+  }
+}