fix: URL persistence in export + cache-busting v4.8.0

- getDocument() now explicitly lists all block fields including url
- loadDocument() initializes url/series_id for backward compat with older JSONs
- Cache-busting query params (?v=4.8) on all static assets
- PDF generator uses block.url directly (proper model field)
- Added 7 new URL tests (model, API, PDF link annotations)
- Version bumped to 4.8.0

app/static/js/app.js

@@ -84,7 +84,18 @@ const App = {
                 date: this.state.event.date_from, // backward compat
             },
             program_types: this.state.program_types.map(pt => ({ ...pt })),
-            blocks: this.state.blocks.map(b => ({ ...b }))
+            blocks: this.state.blocks.map(b => ({
+                id: b.id,
+                date: b.date,
+                start: b.start,
+                end: b.end,
+                title: b.title,
+                type_id: b.type_id,
+                responsible: b.responsible || null,
+                notes: b.notes || null,
+                url: b.url || null,
+                series_id: b.series_id || null,
+            }))
         };
     },
 
@@ -104,7 +115,9 @@ const App = {
         this.state.program_types = (doc.program_types || []).map(pt => ({ ...pt }));
         this.state.blocks = (doc.blocks || []).map(b => ({
             ...b,
-            id: b.id || this.uid()
+            id: b.id || this.uid(),
+            url: b.url || null,           // backward compat: older JSONs lack this
+            series_id: b.series_id || null,
         }));
         this.syncEventToUI();
         this.renderTypes();