[7891] Frontend: Remove feature flag + simplify shared instances component

[n-lark]

Description

This removes the EMBEDDED_DASHBOARD_ENABLED feature flag and cleans up the dashboardRoleOnly list for Instances.vue.

See test plan here: #7891 (comment)

Related Issue(s)

Resolves #7891

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.64%. Comparing base (07e7f78) to head (3c083af).

Additional details and impacted files

@@                      Coverage Diff                      @@
##           7875-applications-dashboards    #7909   +/-   ##
=============================================================
  Coverage                         75.64%   75.64%           
=============================================================
  Files                               432      432           
  Lines                             23083    23083           
  Branches                           6124     6124           
=============================================================
  Hits                              17461    17461           
  Misses                             5622     5622           

Flag	Coverage Δ
backend	75.64% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.