Sync alert and report screenshots with the restyled selects [ignore_release]

[snake14]

Description

Core #25033 restyled the expandable select dropdowns and added a standard drag handle component, which changed how the Custom Alerts form renders. This plugin keeps its own copies of the CustomAlerts_* captures under tests/UI/expected-ui-screenshots/, so its 6.x-dev build has been red since 17 August with five failing captures — four alert-form ones differing by 4698 px and the report error by 1233 px.

CustomAlerts synced its own copies in matomo-org/plugin-CustomAlerts#274 and is green again; MicrosoftTeams had the identical problem and was fixed the same way in matomo-org/plugin-MicrosoftTeams#47. This is the last of the three.

The five captures are regenerated from run 32073288852, the failing run on 6.x-dev at the same commit this branch is based on. No source changes — the rendering is correct, only the baselines were stale. Each was reviewed to confirm it shows a complete, intended render: the error captures still carry their "Slack Channel ID cannot be empty" notification, and the restyled bordered select is visible on the alert condition field.

The same change will break these captures on 5.x-dev when the 5.x backport of #25033 lands.

Issue No

Follow-up to matomo-org/matomo#25033. No separate issue.

Steps to Replicate the Issue

1. Run this plugin's UI tests against Matomo 6.x-dev.
2. Expected: every capture matches its baseline.
3. Actual: should show load a new alert add screen, should show slack channel ID input as disabled as Oauth token not configured, should show slack channel ID input as enabled when Oauth token configured and both should show show error if channelID not set cases fail, differing by 4698 px on the alert-form captures and 1233 px on the report one.

Checklist

• [✖] Tested locally or on demo2/demo3?
• [NA] New test case added/updated?
• [NA] Are all newly added texts included via translation?
• [NA] Are text sanitized properly? (Eg use of v-text v/s v-html for vue)
• [NA] Version bumped?
• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules
• [NA] Documentation updated?