refactor: consolidate formatting utilities and add testing infrastructure

- Replace 8 duplicate formatCurrency functions with shared utility
- Add comprehensive formatter utilities (currency, date, number, etc.)
- Set up Vitest for unit testing with 38 passing tests
- Set up Playwright for E2E testing
- Consolidate database connection to single source (src/utils/db.ts)
- Add auth middleware helpers to reduce code duplication
- Fix display bug: remove spurious minus sign in recent activity amounts
- Add path aliases for cleaner imports ($utils, $models)
- Add project documentation (CODEMAP.md, REFACTORING_PLAN.md)

Test coverage: 38 unit tests passing
Build: successful with no breaking changes

src/models/Exercise.ts

@@ -0,0 +1,100 @@
+import mongoose from 'mongoose';
+
+export interface IExercise {
+  _id?: string;
+  exerciseId: string; // Original ExerciseDB ID
+  name: string;
+  gifUrl: string; // URL to the exercise animation GIF
+  bodyPart: string; // e.g., "chest", "back", "legs"
+  equipment: string; // e.g., "barbell", "dumbbell", "bodyweight"
+  target: string; // Primary target muscle
+  secondaryMuscles: string[]; // Secondary muscles worked
+  instructions: string[]; // Step-by-step instructions
+  category?: string; // Custom categorization
+  difficulty?: 'beginner' | 'intermediate' | 'advanced';
+  isActive?: boolean; // Allow disabling exercises
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+const ExerciseSchema = new mongoose.Schema(
+  {
+    exerciseId: {
+      type: String,
+      required: true,
+      unique: true
+    },
+    name: {
+      type: String,
+      required: true,
+      trim: true,
+      index: true // For fast searching
+    },
+    gifUrl: {
+      type: String,
+      required: true
+    },
+    bodyPart: {
+      type: String,
+      required: true,
+      lowercase: true,
+      index: true // For filtering by body part
+    },
+    equipment: {
+      type: String,
+      required: true,
+      lowercase: true,
+      index: true // For filtering by equipment
+    },
+    target: {
+      type: String,
+      required: true,
+      lowercase: true,
+      index: true // For filtering by target muscle
+    },
+    secondaryMuscles: {
+      type: [String],
+      default: []
+    },
+    instructions: {
+      type: [String],
+      required: true,
+      validate: {
+        validator: function(instructions: string[]) {
+          return instructions.length > 0;
+        },
+        message: 'Exercise must have at least one instruction'
+      }
+    },
+    category: {
+      type: String,
+      trim: true
+    },
+    difficulty: {
+      type: String,
+      enum: ['beginner', 'intermediate', 'advanced'],
+      default: 'intermediate'
+    },
+    isActive: {
+      type: Boolean,
+      default: true
+    }
+  },
+  {
+    timestamps: true,
+    toJSON: { virtuals: true },
+    toObject: { virtuals: true }
+  }
+);
+
+// Text search index for exercise names and instructions
+ExerciseSchema.index({
+  name: 'text',
+  instructions: 'text'
+});
+
+// Compound indexes for common queries
+ExerciseSchema.index({ bodyPart: 1, equipment: 1 });
+ExerciseSchema.index({ target: 1, isActive: 1 });
+
+export const Exercise = mongoose.model<IExercise>("Exercise", ExerciseSchema);