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/WorkoutSession.ts

@@ -0,0 +1,143 @@
+import mongoose from 'mongoose';
+
+export interface ICompletedSet {
+  reps: number;
+  weight?: number;
+  rpe?: number; // Rate of Perceived Exertion (1-10)
+  completed: boolean;
+  notes?: string;
+}
+
+export interface ICompletedExercise {
+  name: string;
+  sets: ICompletedSet[];
+  restTime?: number;
+  notes?: string;
+}
+
+export interface IWorkoutSession {
+  _id?: string;
+  templateId?: string; // Reference to WorkoutTemplate if based on template
+  templateName?: string; // Snapshot of template name for history
+  name: string;
+  exercises: ICompletedExercise[];
+  startTime: Date;
+  endTime?: Date;
+  duration?: number; // Duration in minutes
+  notes?: string;
+  createdBy: string; // username/nickname of the person who performed the workout
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+const CompletedSetSchema = new mongoose.Schema({
+  reps: {
+    type: Number,
+    required: true,
+    min: 0,
+    max: 1000
+  },
+  weight: {
+    type: Number,
+    min: 0,
+    max: 1000 // kg
+  },
+  rpe: {
+    type: Number,
+    min: 1,
+    max: 10
+  },
+  completed: {
+    type: Boolean,
+    default: false
+  },
+  notes: {
+    type: String,
+    trim: true,
+    maxlength: 200
+  }
+});
+
+const CompletedExerciseSchema = new mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  sets: {
+    type: [CompletedSetSchema],
+    required: true
+  },
+  restTime: {
+    type: Number,
+    default: 120, // 2 minutes in seconds
+    min: 10,
+    max: 600 // max 10 minutes rest
+  },
+  notes: {
+    type: String,
+    trim: true,
+    maxlength: 500
+  }
+});
+
+const WorkoutSessionSchema = new mongoose.Schema(
+  {
+    templateId: {
+      type: mongoose.Schema.Types.ObjectId,
+      ref: 'WorkoutTemplate'
+    },
+    templateName: {
+      type: String,
+      trim: true
+    },
+    name: {
+      type: String,
+      required: true,
+      trim: true,
+      maxlength: 100
+    },
+    exercises: {
+      type: [CompletedExerciseSchema],
+      required: true,
+      validate: {
+        validator: function(exercises: ICompletedExercise[]) {
+          return exercises.length > 0;
+        },
+        message: 'A workout session must have at least one exercise'
+      }
+    },
+    startTime: {
+      type: Date,
+      required: true,
+      default: Date.now
+    },
+    endTime: {
+      type: Date
+    },
+    duration: {
+      type: Number, // in minutes
+      min: 0
+    },
+    notes: {
+      type: String,
+      trim: true,
+      maxlength: 1000
+    },
+    createdBy: {
+      type: String,
+      required: true,
+      trim: true
+    }
+  },
+  {
+    timestamps: true,
+    toJSON: { virtuals: true },
+    toObject: { virtuals: true }
+  }
+);
+
+WorkoutSessionSchema.index({ createdBy: 1, startTime: -1 });
+WorkoutSessionSchema.index({ templateId: 1 });
+
+export const WorkoutSession = mongoose.model<IWorkoutSession>("WorkoutSession", WorkoutSessionSchema);