Escape editor notification messages

[sol-hermes85]

Hi maintainers, thanks again for the work on DeTTECT.

This fixes a small client-side security issue in the editor notification component. Notification messages were rendered with v-html, so message text containing HTML could be interpreted by the browser. I checked the current notification call sites and did not find any notification messages that rely on HTML formatting, so this switches message rendering back to Vue's escaped text interpolation.

Changes:

• render notification message values as escaped text
• add a small regression test to keep v-html out of notification messages

Validation:

• python -m unittest tests.test_editor_notifications -v
• python -m unittest discover -s tests -v
• python -m compileall -q tests/test_editor_notifications.py
• git diff --check
• searched editor/src for v-html, no remaining matches

Note: I also tried to run the editor lint command, but dependency installation fails locally because node-sass@6.0.1 does not build on Node.js 22. I have kept this PR limited to the notification rendering fix.