Add complete database schema and ORM models

Schema (002_tables.sql):
- users: accounts with nick, password hash, timestamps
- auth_tokens: per-device tokens with expiry, linked to users
- channels: chat rooms with topic and mode flags
- channel_members: membership with per-user modes (+o, +v)
- messages: channel/DM history with structured JSON meta
- message_queue: per-user pending delivery queue
- sessions: server-held session state with idle timeout
- server_links: federation peer configuration

Models (internal/models/):
- All models embed Base for database access
- Relation methods on models: User.Channels(), User.QueuedMessages(),
  Channel.Members(), Channel.RecentMessages(), ChannelMember.User(),
  ChannelMember.Channel(), AuthToken.User(), Session.User()
- IDs are UUIDs (TEXT), not auto-increment integers
- JSON tags use camelCase per lint rules

All tables verified: migrations apply cleanly, 0 lint issues.

internal/models/user.go

@@ -0,0 +1,92 @@
+package models
+
+import (
+	"context"
+	"time"
+)
+
+// User represents a registered user account.
+type User struct {
+	Base
+
+	ID           string     `json:"id"`
+	Nick         string     `json:"nick"`
+	PasswordHash string     `json:"-"`
+	CreatedAt    time.Time  `json:"createdAt"`
+	UpdatedAt    time.Time  `json:"updatedAt"`
+	LastSeenAt   *time.Time `json:"lastSeenAt,omitempty"`
+}
+
+// Channels returns all channels the user is a member of.
+func (u *User) Channels(ctx context.Context) ([]*Channel, error) {
+	rows, err := u.GetDB().QueryContext(ctx, `
+		SELECT c.id, c.name, c.topic, c.modes, c.created_at, c.updated_at
+		FROM channels c
+		JOIN channel_members cm ON cm.channel_id = c.id
+		WHERE cm.user_id = ?
+		ORDER BY c.name`,
+		u.ID,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var channels []*Channel
+
+	for rows.Next() {
+		c := &Channel{}
+		c.SetDB(u.db)
+
+		err = rows.Scan(
+			&c.ID, &c.Name, &c.Topic, &c.Modes,
+			&c.CreatedAt, &c.UpdatedAt,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		channels = append(channels, c)
+	}
+
+	return channels, rows.Err()
+}
+
+// QueuedMessages returns undelivered messages for this user.
+func (u *User) QueuedMessages(ctx context.Context) ([]*Message, error) {
+	rows, err := u.GetDB().QueryContext(ctx, `
+		SELECT m.id, m.ts, m.from_user_id, m.from_nick,
+		       m.target, m.type, m.body, m.meta, m.created_at
+		FROM messages m
+		JOIN message_queue mq ON mq.message_id = m.id
+		WHERE mq.user_id = ?
+		ORDER BY mq.queued_at ASC`,
+		u.ID,
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	defer func() { _ = rows.Close() }()
+
+	var messages []*Message
+
+	for rows.Next() {
+		msg := &Message{}
+		msg.SetDB(u.db)
+
+		err = rows.Scan(
+			&msg.ID, &msg.Timestamp, &msg.FromUserID,
+			&msg.FromNick, &msg.Target, &msg.Type,
+			&msg.Body, &msg.Meta, &msg.CreatedAt,
+		)
+		if err != nil {
+			return nil, err
+		}
+
+		messages = append(messages, msg)
+	}
+
+	return messages, rows.Err()
+}