feat: v3.0 - canvas editor, JSON-only, no Excel, new UI

- Remove all Excel code (import, export, template, pandas, openpyxl)
- New canvas-based schedule editor with drag & drop (interact.js)
- Modern 3-panel UI: sidebar, canvas, documentation tab
- New data model: Block with id/date/start/end, ProgramType with id/name/color
- Clean API: GET /api/health, POST /api/validate, GET /api/sample, POST /api/generate-pdf
- Rewritten PDF generator using ScenarioDocument directly (no DataFrame)
- Professional PDF output: dark header, colored blocks, merged cells, legend, footer
- Sample JSON: "Zimní výjezd oddílu" with 11 blocks, 3 program types
- 30 tests passing (API, core models, PDF generation)

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

app/static/js/export.js

@@ -1,33 +1,31 @@
 /**
- * JSON import/export for Scenar Creator.
+ * JSON import/export for Scenar Creator v3.
  */
 
 function exportJson() {
-    if (!window.currentDocument) {
-        showStatus('No document to export', 'error');
+    const doc = App.getDocument();
+    if (!doc) {
+        App.toast('Žádný scénář k exportu', 'error');
         return;
     }
-    const json = JSON.stringify(window.currentDocument, null, 2);
+    const json = JSON.stringify(doc, null, 2);
     const blob = new Blob([json], { type: 'application/json' });
     API.downloadBlob(blob, 'scenar_export.json');
+    App.toast('JSON exportován', 'success');
 }
 
-function handleJsonImport(event) {
-    const file = event.target.files[0];
-    if (!file) return;
-
+function importJson(file) {
     const reader = new FileReader();
     reader.onload = function (e) {
         try {
             const doc = JSON.parse(e.target.result);
             if (!doc.event || !doc.blocks || !doc.program_types) {
-                throw new Error('Invalid ScenarioDocument format');
+                throw new Error('Neplatný formát ScenarioDocument');
             }
-            window.currentDocument = doc;
-            showImportedDocument(doc);
-            showStatus('JSON imported successfully', 'success');
+            App.loadDocument(doc);
+            App.toast('JSON importován', 'success');
         } catch (err) {
-            showStatus('JSON import error: ' + err.message, 'error');
+            App.toast('Chyba importu: ' + err.message, 'error');
         }
     };
     reader.readAsText(file);