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/WorkoutTemplate.ts

@@ -0,0 +1,112 @@
+import mongoose from 'mongoose';
+
+export interface ISet {
+  reps: number;
+  weight?: number;
+  rpe?: number; // Rate of Perceived Exertion (1-10)
+}
+
+export interface IExercise {
+  name: string;
+  sets: ISet[];
+  restTime?: number; // Rest time in seconds, defaults to 120 (2 minutes)
+}
+
+export interface IWorkoutTemplate {
+  _id?: string;
+  name: string;
+  description?: string;
+  exercises: IExercise[];
+  createdBy: string; // username/nickname of the person who created the template
+  isPublic?: boolean; // whether other users can see/use this template
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+const SetSchema = new mongoose.Schema({
+  reps: {
+    type: Number,
+    required: true,
+    min: 1,
+    max: 1000
+  },
+  weight: {
+    type: Number,
+    min: 0,
+    max: 1000 // kg
+  },
+  rpe: {
+    type: Number,
+    min: 1,
+    max: 10
+  }
+});
+
+const ExerciseSchema = new mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  sets: {
+    type: [SetSchema],
+    required: true,
+    validate: {
+      validator: function(sets: ISet[]) {
+        return sets.length > 0;
+      },
+      message: 'An exercise must have at least one set'
+    }
+  },
+  restTime: {
+    type: Number,
+    default: 120, // 2 minutes in seconds
+    min: 10,
+    max: 600 // max 10 minutes rest
+  }
+});
+
+const WorkoutTemplateSchema = new mongoose.Schema(
+  {
+    name: {
+      type: String,
+      required: true,
+      trim: true,
+      maxlength: 100
+    },
+    description: {
+      type: String,
+      trim: true,
+      maxlength: 500
+    },
+    exercises: {
+      type: [ExerciseSchema],
+      required: true,
+      validate: {
+        validator: function(exercises: IExercise[]) {
+          return exercises.length > 0;
+        },
+        message: 'A workout template must have at least one exercise'
+      }
+    },
+    createdBy: {
+      type: String,
+      required: true,
+      trim: true
+    },
+    isPublic: {
+      type: Boolean,
+      default: false
+    }
+  },
+  {
+    timestamps: true,
+    toJSON: { virtuals: true },
+    toObject: { virtuals: true }
+  }
+);
+
+WorkoutTemplateSchema.index({ createdBy: 1 });
+WorkoutTemplateSchema.index({ name: 1, createdBy: 1 });
+
+export const WorkoutTemplate = mongoose.model<IWorkoutTemplate>("WorkoutTemplate", WorkoutTemplateSchema);