Fix code review feedback items 1-6, 8-10

- Item 1: Extract GetUserByID/GetChannelByID lookup methods, use from relation methods
- Item 2: Initialize slices with literals so JSON gets [] not null
- Item 3: Populate CreatedAt/UpdatedAt with time.Now() on all Create methods
- Item 4: Wrap each migration's SQL + recording in a transaction
- Item 5: Check error from res.LastInsertId() in QueueMessage
- Item 6: Add DequeueMessages and AckMessages methods
- Item 8: Add GetUserByNick, GetUserByToken, DeleteAuthToken, UpdateUserLastSeen
- Item 9: Run PRAGMA foreign_keys = ON on every new connection
- Item 10: Builds clean, all tests pass

internal/models/session.go

@@ -2,6 +2,7 @@ package models
 
 import (
 	"context"
+	"fmt"
 	"time"
 )
 
@@ -18,20 +19,9 @@ type Session struct {
 
 // User returns the user who owns this session.
 func (s *Session) User(ctx context.Context) (*User, error) {
-	u := &User{}
-	u.SetDB(s.db)
-
-	err := s.GetDB().QueryRowContext(ctx, `
-		SELECT id, nick, password_hash, created_at, updated_at, last_seen_at
-		FROM users WHERE id = ?`,
-		s.UserID,
-	).Scan(
-		&u.ID, &u.Nick, &u.PasswordHash,
-		&u.CreatedAt, &u.UpdatedAt, &u.LastSeenAt,
-	)
-	if err != nil {
-		return nil, err
+	if ul := s.GetUserLookup(); ul != nil {
+		return ul.GetUserByID(ctx, s.UserID)
 	}
 
-	return u, nil
+	return nil, fmt.Errorf("user lookup not available")
 }