feat: add session replay with terminal playback via xterm.js

Persist byte-level I/O events from SSH sessions to SQLite and add a web
UI to replay them with original timing. Events are buffered in memory
and flushed every 2s to avoid blocking SSH I/O on database writes.

- Add session_events table (migration 002)
- Add SessionEvent type and storage methods (SQLite + MemoryStore)
- Change RecordingChannel to support multiple callbacks
- Add EventRecorder for buffered event persistence
- Add session detail page with xterm.js terminal replay
- Add /api/sessions/{id}/events JSON endpoint
- Linkify session IDs in dashboard and active sessions
- Vendor xterm.js v5.3.0

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

internal/web/templates.go

@@ -10,8 +10,13 @@ import (
 //go:embed templates/*.html templates/fragments/*.html
 var templateFS embed.FS
 
-func loadTemplates() (*template.Template, error) {
-	funcMap := template.FuncMap{
+type templateSet struct {
+	dashboard     *template.Template
+	sessionDetail *template.Template
+}
+
+func templateFuncMap() template.FuncMap {
+	return template.FuncMap{
 		"formatTime": func(t time.Time) string {
 			return t.Format("2006-01-02 15:04:05 UTC")
 		},
@@ -40,11 +45,31 @@ func loadTemplates() (*template.Template, error) {
 			return fmt.Sprintf("%.0f%%", *f*100)
 		},
 	}
+}
 
-	return template.New("").Funcs(funcMap).ParseFS(templateFS,
+func loadTemplates() (*templateSet, error) {
+	funcMap := templateFuncMap()
+
+	dashboard, err := template.New("").Funcs(funcMap).ParseFS(templateFS,
 		"templates/layout.html",
 		"templates/dashboard.html",
 		"templates/fragments/stats.html",
 		"templates/fragments/active_sessions.html",
 	)
+	if err != nil {
+		return nil, fmt.Errorf("parsing dashboard templates: %w", err)
+	}
+
+	sessionDetail, err := template.New("").Funcs(funcMap).ParseFS(templateFS,
+		"templates/layout.html",
+		"templates/session_detail.html",
+	)
+	if err != nil {
+		return nil, fmt.Errorf("parsing session detail templates: %w", err)
+	}
+
+	return &templateSet{
+		dashboard:     dashboard,
+		sessionDetail: sessionDetail,
+	}, nil
 }