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/MarioKartTournament.ts

@@ -0,0 +1,228 @@
+import mongoose from 'mongoose';
+
+export interface IContestant {
+  _id?: string;
+  name: string;
+  seed?: number; // For bracket seeding
+  dnf?: boolean; // Did Not Finish - marked as inactive mid-tournament
+}
+
+export interface IRound {
+  roundNumber: number;
+  scores: Map<string, number>; // contestantId -> score
+  completedAt?: Date;
+}
+
+export interface IGroupMatch {
+  _id?: string;
+  contestantIds: string[]; // All contestants in this match
+  rounds: IRound[];
+  completed: boolean;
+}
+
+export interface IGroup {
+  _id?: string;
+  name: string;
+  contestantIds: string[]; // References to contestants
+  matches: IGroupMatch[];
+  standings?: { contestantId: string; totalScore: number; position: number }[];
+}
+
+export interface IBracketMatch {
+  _id?: string;
+  contestantIds: string[]; // Array of contestant IDs competing in this match
+  rounds: IRound[];
+  winnerId?: string;
+  completed: boolean;
+}
+
+export interface IBracketRound {
+  roundNumber: number; // 1 = finals, 2 = semis, 3 = quarters, etc.
+  name: string; // "Finals", "Semi-Finals", etc.
+  matches: IBracketMatch[];
+}
+
+export interface IBracket {
+  rounds: IBracketRound[];
+}
+
+export interface IMarioKartTournament {
+  _id?: string;
+  name: string;
+  status: 'setup' | 'group_stage' | 'bracket' | 'completed';
+  contestants: IContestant[];
+  groups: IGroup[];
+  bracket?: IBracket;
+  runnersUpBracket?: IBracket;
+  roundsPerMatch: number; // How many rounds in each match
+  matchSize: number; // How many contestants compete simultaneously (default 2 for 1v1)
+  createdBy: string;
+  createdAt?: Date;
+  updatedAt?: Date;
+}
+
+const RoundSchema = new mongoose.Schema({
+  roundNumber: {
+    type: Number,
+    required: true,
+    min: 1
+  },
+  scores: {
+    type: Map,
+    of: Number,
+    required: true
+  },
+  completedAt: {
+    type: Date
+  }
+});
+
+const GroupMatchSchema = new mongoose.Schema({
+  contestantIds: {
+    type: [String],
+    required: true
+  },
+  rounds: {
+    type: [RoundSchema],
+    default: []
+  },
+  completed: {
+    type: Boolean,
+    default: false
+  }
+});
+
+const GroupSchema = new mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  contestantIds: {
+    type: [String],
+    required: true
+  },
+  matches: {
+    type: [GroupMatchSchema],
+    default: []
+  },
+  standings: [{
+    contestantId: String,
+    totalScore: Number,
+    position: Number
+  }]
+});
+
+const BracketMatchSchema = new mongoose.Schema({
+  contestantIds: {
+    type: [String],
+    default: [],
+    required: false
+  },
+  rounds: {
+    type: [RoundSchema],
+    default: []
+  },
+  winnerId: {
+    type: String,
+    required: false
+  },
+  completed: {
+    type: Boolean,
+    default: false
+  }
+}, { _id: true, minimize: false });
+
+const BracketRoundSchema = new mongoose.Schema({
+  roundNumber: {
+    type: Number,
+    required: true
+  },
+  name: {
+    type: String,
+    required: true
+  },
+  matches: {
+    type: [BracketMatchSchema],
+    required: true
+  }
+}, { _id: true, minimize: false });
+
+const BracketSchema = new mongoose.Schema({
+  rounds: {
+    type: [BracketRoundSchema],
+    default: []
+  }
+}, { _id: true, minimize: false });
+
+const ContestantSchema = new mongoose.Schema({
+  name: {
+    type: String,
+    required: true,
+    trim: true
+  },
+  seed: {
+    type: Number
+  },
+  dnf: {
+    type: Boolean,
+    default: false
+  }
+});
+
+const MarioKartTournamentSchema = new mongoose.Schema(
+  {
+    name: {
+      type: String,
+      required: true,
+      trim: true,
+      maxlength: 200
+    },
+    status: {
+      type: String,
+      enum: ['setup', 'group_stage', 'bracket', 'completed'],
+      default: 'setup'
+    },
+    contestants: {
+      type: [ContestantSchema],
+      default: []
+    },
+    groups: {
+      type: [GroupSchema],
+      default: []
+    },
+    bracket: {
+      type: BracketSchema
+    },
+    runnersUpBracket: {
+      type: BracketSchema
+    },
+    roundsPerMatch: {
+      type: Number,
+      default: 3,
+      min: 1,
+      max: 10
+    },
+    matchSize: {
+      type: Number,
+      default: 2,
+      min: 2,
+      max: 12
+    },
+    createdBy: {
+      type: String,
+      required: true,
+      trim: true
+    }
+  },
+  {
+    timestamps: true,
+    toJSON: { virtuals: true },
+    toObject: { virtuals: true }
+  }
+);
+
+MarioKartTournamentSchema.index({ createdBy: 1, createdAt: -1 });
+
+export const MarioKartTournament = mongoose.models.MarioKartTournament ||
+  mongoose.model<IMarioKartTournament>("MarioKartTournament", MarioKartTournamentSchema);