fix(core): don't hijack Ctrl+F in editors or behind modals

[pringelmann]

• Resolves: Search for word inside page is impossible #63409

Summary

Unified search bound its own keydown listener that never checked the event target or open modals, so Ctrl+F inside a Text document opened search instead of the browser's find bar. useHotKey already guards both, so this uses it instead of duplicating that logic in core.

Behaviour changes

• Ctrl+F in an editor or input now goes to the browser. Same behind an open modal.
• Ctrl+K works again on /settings/users, /settings/apps and /apps/deck. It was checking the Ctrl+F opt-out, which nothing on that list uses for Ctrl+K, so Firefox took the key. Pre-existing bug.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes (no visual change)
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI (tests, reviewed by me)

[pringelmann]

/backport to stable34

[pringelmann]

/compile rebase

[pringelmann]

/compile rebase

[susnux]

/backport to stable35

[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/63541/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 fe4fae0e 5e26b1ee

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/63541/stable34

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

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