Add embedded web chat client with C2S HTTP API

- New DB schema: users, channel_members, messages tables (migration 003)
- Full C2S HTTP API: register, channels, messages, DMs, polling
- Preact SPA embedded via embed.FS, served at GET /
- IRC-style UI: tab bar, channel messages, user list, DM tabs, /commands
- Dark theme, responsive, esbuild-bundled (~19KB)
- Polling-based message delivery (1.5s interval)
- Commands: /join, /part, /msg, /nick

internal/handlers/handlers.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net/http"
 
+	"git.eeqj.de/sneak/chat/internal/config"
 	"git.eeqj.de/sneak/chat/internal/db"
 	"git.eeqj.de/sneak/chat/internal/globals"
 	"git.eeqj.de/sneak/chat/internal/healthcheck"
@@ -20,6 +21,7 @@ type Params struct {
 
 	Logger      *logger.Logger
 	Globals     *globals.Globals
+	Config      *config.Config
 	Database    *db.Database
 	Healthcheck *healthcheck.Healthcheck
 }