feat(smart-crop): overhaul with face detection, social presets, and 3 modes

Replace the confusing 2-mode smart crop with a clear 3-mode system:
- Subject Focus: Sharp attention/entropy saliency crop with social media presets
- Face Focus: MediaPipe face detection with headshot framing presets
- Auto Trim: Border removal with optional pad-to-square

Adds detectFaces() to AI package, face preset constants, backward
compatibility for old mode names, and comprehensive integration tests.

packages/shared/src/constants.ts

@@ -132,7 +132,7 @@ export const TOOLS: Tool[] = [
   {
     id: "erase-object",
     name: "Object Eraser",
-    description: "Paint over unwanted elements",
+    description: "Remove unwanted objects with AI",
     category: "ai",
     icon: "Wand2",
     route: "/erase-object",
@@ -156,7 +156,7 @@ export const TOOLS: Tool[] = [
   {
     id: "smart-crop",
     name: "Smart Crop",
-    description: "AI detects subject and crops optimally",
+    description: "Smart subject, face, or trim-based cropping",
     category: "ai",
     icon: "Focus",
     route: "/smart-crop",
@@ -354,6 +354,19 @@ export const SOCIAL_MEDIA_PRESETS: SocialMediaPreset[] = [
   { platform: "Threads", name: "Post Image", width: 1080, height: 1080 },
 ];
 
+export interface SmartCropFacePreset {
+  id: string;
+  label: string;
+  multiplier: number;
+}
+
+export const SMART_CROP_FACE_PRESETS: SmartCropFacePreset[] = [
+  { id: "closeup", label: "Close-up", multiplier: 1.8 },
+  { id: "head-shoulders", label: "Head & Shoulders", multiplier: 2.8 },
+  { id: "upper-body", label: "Upper Body", multiplier: 4.5 },
+  { id: "half-body", label: "Half Body", multiplier: 7.0 },
+];
+
 export const APP_VERSION = "1.14.0";
 
 /**