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>

internal/web/templates.go

@@ -0,0 +1,37 @@
+package web
+
+import (
+	"embed"
+	"html/template"
+	"time"
+)
+
+//go:embed templates/*.html templates/fragments/*.html
+var templateFS embed.FS
+
+func loadTemplates() (*template.Template, error) {
+	funcMap := template.FuncMap{
+		"formatTime": func(t time.Time) string {
+			return t.Format("2006-01-02 15:04:05 UTC")
+		},
+		"truncateID": func(id string) string {
+			if len(id) > 8 {
+				return id[:8]
+			}
+			return id
+		},
+		"derefTime": func(t *time.Time) time.Time {
+			if t == nil {
+				return time.Time{}
+			}
+			return *t
+		},
+	}
+
+	return template.New("").Funcs(funcMap).ParseFS(templateFS,
+		"templates/layout.html",
+		"templates/dashboard.html",
+		"templates/fragments/stats.html",
+		"templates/fragments/active_sessions.html",
+	)
+}