fix(embed): guard unavailable search commands

[joshtrichards]

📝 Summary

• Resolves: won't work with rich editing off collectives#2434

When rich_editing_enabled = 0, the collaborative editor created through Text’s integration (embed) API uses the plain-text editor. This editor does not include the Search extension, so the related commands are unavailable.

Guard the embedded editor API calls to:

• setSearchQuery
• searchNext
• searchPrevious

When these commands are unavailable, the methods now safely behave as no-ops instead of throwing an exception.

This allows integrations such as Collectives to finish loading when rich editing is disabled.

🖼️ Screenshots

🏚️ Before	🏡 After
B	A

🚧 TODO

• ...

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI tools
• The AI-generated content was reviewed, comprehended and tested by a human

[mejo-]

Thanks @joshtrichards. Tested locally and works well ☺️

[mejo-]

/backport to stable34

[backportbot]

The backport to stable34 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable34
git pull origin stable34

# Create the new backport branch
git checkout -b backport/8970/stable34

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 286926a6

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/8970/stable34

Error: Failed to check for changes with origin/stable34: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[mejo-]

/backport to stable33

[backportbot]

The backport to stable33 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable33
git pull origin stable33

# Create the new backport branch
git checkout -b backport/8970/stable33

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 286926a6

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/8970/stable33

Error: Failed to check for changes with origin/stable33: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[mejo-]

Manual backport to stable34 at #8981.