chore: update @libresign/pdf-elements to v1.2.0

Updates to v1.2.0 which includes:
- first-class pdf-elements:adding-ended event for interactive placement
- event payload types (placed/cancelled) exported from package API
- full test coverage for both event flows

This aligns LibreSign to use the new stable event contract from pdf-elements,
complementing the mobile signature placement flow refactorings in this PR.

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

package-lock.json

@@ -30,7 +30,7 @@
     "@codemirror/state": "^6.6.0",
     "@codemirror/view": "^6.41.0",
     "@fontsource/dancing-script": "^5.2.8",
-    "@libresign/pdf-elements": "^1.1.6",
+    "@libresign/pdf-elements": "^1.2.0",
     "@marionebl/option": "^1.0.8",
     "@mdi/js": "^7.4.47",
     "@mdi/svg": "^7.4.47",