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/db/db.go

@@ -11,7 +11,6 @@ import (
 	"sort"
 	"strconv"
 	"strings"
-	"time"
 
 	"git.eeqj.de/sneak/chat/internal/config"
 	"git.eeqj.de/sneak/chat/internal/logger"
@@ -51,19 +50,9 @@ func (s *Database) GetDB() *sql.DB {
 	return s.db
 }
 
-// NewChannel creates a Channel model instance with the db reference injected.
-func (s *Database) NewChannel(id int64, name, topic, modes string, createdAt, updatedAt time.Time) *models.Channel {
-	c := &models.Channel{
-		ID:        id,
-		Name:      name,
-		Topic:     topic,
-		Modes:     modes,
-		CreatedAt: createdAt,
-		UpdatedAt: updatedAt,
-	}
-	c.SetDB(s)
-
-	return c
+// Hydrate injects the database reference into any model that embeds Base.
+func (s *Database) Hydrate(m interface{ SetDB(d models.DB) }) {
+	m.SetDB(s)
 }
 
 // New creates a new Database instance and registers lifecycle hooks.