fix: i18n translations and annotation property changes on selected objects

- Complete English translation catalog (44 entries fixed/added)
- Fix Fabric.js Group cache invalidation (active.dirty = true) so color,
  thickness and line-dash changes are visible on selected markers/arrows
- Fix Italian .po placeholder mismatch (%(detail)s -> %(error)s)
- Bump annotation-editor.js cache buster to v8

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

client/static/js/annotation-editor.js

@@ -144,6 +144,7 @@ function annotationEditor() {
               active.set('stroke', e.detail.color);
               active.areaColor = e.detail.color;
             }
+            active.dirty = true;
             self.canvas.renderAll();
             self.isDirty = true;
             window.dispatchEvent(new CustomEvent('annotations-changed', { detail: { json: self.getAnnotationsJson() } }));
@@ -166,6 +167,7 @@ function annotationEditor() {
               active.set('strokeWidth', e.detail.width);
               active.areaStrokeWidth = e.detail.width;
             }
+            active.dirty = true;
             self.canvas.renderAll();
             self.isDirty = true;
             window.dispatchEvent(new CustomEvent('annotations-changed', { detail: { json: self.getAnnotationsJson() } }));
@@ -188,6 +190,7 @@ function annotationEditor() {
               active.set('strokeDashArray', dashArr);
               active.areaLineDash = self.currentLineDash.slice();
             }
+            active.dirty = true;
             self.canvas.renderAll();
             self.isDirty = true;
             window.dispatchEvent(new CustomEvent('annotations-changed', { detail: { json: self.getAnnotationsJson() } }));