Phase 1: database schema, migrations, repository, user seeding

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/models/models.go

@@ -0,0 +1,53 @@
+package models
+
+import (
+	"database/sql"
+	"time"
+)
+
+type User struct {
+	ID           int64
+	Name         string
+	PasswordHash string
+	CreatedAt    time.Time
+}
+
+type Question struct {
+	ID        string // sha256(text)[:8 bytes] hex = 16 chars
+	Text      string
+	Source    string
+	CreatedAt time.Time
+}
+
+type Answer struct {
+	ID         int64
+	QuestionID string
+	Text       string
+	IsCorrect  bool
+	Position   int
+}
+
+type Test struct {
+	ID          int64
+	UserID      int64
+	CreatedAt   time.Time
+	CompletedAt sql.NullTime
+	NQuestions  int
+	QuestionIDs []string // unmarshaled from JSON
+}
+
+type TestAnswer struct {
+	TestID           int64
+	QuestionID       string
+	SelectedAnswerID sql.NullInt64
+	IsCorrect        sql.NullBool
+	AnsweredAt       sql.NullTime
+}
+
+type UserQuestionStat struct {
+	UserID       int64
+	QuestionID   string
+	TimesSeen    int
+	TimesCorrect int
+	LastSeenAt   sql.NullTime
+}