feat(workspace): journal panel toggle, view kept across tabs, sections nest under headings

- the journal opens as a framed panel and closes on a second click,
  returning to the previous note; journal state and the last regular note
  survive tab switches, the fallback note is never a journal day
- pasted and imported markdown nests content under its heading (H2 below
  H1), Enter on a heading creates a child, '- ' / '* ' / '+ ' start a bullet

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/import_markdown_test.go

@@ -4,6 +4,7 @@ import (
 	"archive/zip"
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -219,3 +220,18 @@ func TestImportBackupZip(t *testing.T) {
 	}
 	checkRestored(t, store, ben)
 }
+
+func TestMarkdownHeadingsNestTheirSections(t *testing.T) {
+	blocks := MarkdownToBlocks("# Projekt\nEinleitung\n## Teil A\n- Punkt\n  - Unterpunkt\n## Teil B\n1. Erstens\n# Anhang\nText")
+	var got []string
+	for _, b := range blocks {
+		got = append(got, fmt.Sprintf("%d:%s:%s", b.Level, b.Type, b.Content))
+	}
+	want := []string{
+		"0:h1:Projekt", "1:bullet:Einleitung", "1:h2:Teil A", "2:bullet:Punkt", "3:bullet:Unterpunkt",
+		"1:h2:Teil B", "2:numbered:Erstens", "0:h1:Anhang", "1:bullet:Text",
+	}
+	if strings.Join(got, "|") != strings.Join(want, "|") {
+		t.Fatalf("got  %v\nwant %v", got, want)
+	}
+}