feat: add minimal web dashboard with stats, top credentials, and sessions

Implements Phase 1.5 — an embedded web UI using Go templates, Pico CSS
(dark theme), and htmx for auto-refreshing stats and active sessions.

Adds read query methods to the Store interface (GetDashboardStats,
GetTopUsernames, GetTopPasswords, GetTopIPs, GetRecentSessions) with
implementations for both SQLite and MemoryStore. Introduces the
internal/web package with server, handlers, templates, and tests.
Web server is opt-in via [web] config section and runs alongside
SSH with graceful shutdown. Bumps version to 0.2.0.

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

cmd/oubliette/main.go

@@ -2,18 +2,22 @@ package main
 
 import (
 	"context"
+	"errors"
 	"flag"
 	"log/slog"
+	"net/http"
 	"os"
 	"os/signal"
+	"sync"
 	"syscall"
 
 	"git.t-juice.club/torjus/oubliette/internal/config"
 	"git.t-juice.club/torjus/oubliette/internal/server"
 	"git.t-juice.club/torjus/oubliette/internal/storage"
+	"git.t-juice.club/torjus/oubliette/internal/web"
 )
 
-const Version = "0.1.0"
+const Version = "0.2.0"
 
 func main() {
 	configPath := flag.String("config", "oubliette.toml", "path to config file")
@@ -65,10 +69,44 @@ func main() {
 		os.Exit(1)
 	}
 
+	var wg sync.WaitGroup
+
+	// Start web server if enabled.
+	if cfg.Web.Enabled {
+		webHandler, err := web.NewServer(store, logger.With("component", "web"))
+		if err != nil {
+			logger.Error("failed to create web server", "err", err)
+			os.Exit(1)
+		}
+
+		httpServer := &http.Server{
+			Addr:    cfg.Web.ListenAddr,
+			Handler: webHandler,
+		}
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			logger.Info("web server listening", "addr", cfg.Web.ListenAddr)
+			if err := httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
+				logger.Error("web server error", "err", err)
+			}
+		}()
+
+		// Graceful shutdown on context cancellation.
+		go func() {
+			<-ctx.Done()
+			if err := httpServer.Shutdown(context.Background()); err != nil {
+				logger.Error("web server shutdown error", "err", err)
+			}
+		}()
+	}
+
 	if err := srv.ListenAndServe(ctx); err != nil {
 		logger.Error("server error", "err", err)
 		os.Exit(1)
 	}
 
+	wg.Wait()
 	logger.Info("server stopped")
 }