Add Czech translations for external braille displays

[matejplch626-afk]

Summary

Adds Czech translations for the new external braille display UI introduced for displays provided by other apps.

The change translates all 11 current external_display* / external_displays* strings from braille/brailledisplay/src/phone/res/values/strings.xml and refreshes only the corresponding Czech MissingTranslation entries in lint-baseline.xml.

Validation

The baseline update was derived from the actual :lintPhoneDebug XML report and matched by resource key + original source XML file. The validation required exactly 11 matching Czech baseline entries and rejected unrelated changes.

Before opening this PR, the branch passed:

• ./gradlew assembleDebug --console=plain
• ./gradlew testPhoneDebugUnitTest --console=plain
• ./gradlew :lintPhoneDebug --console=plain

The final diff against upstream master contains only the Czech resource file and the targeted lint baseline refresh; temporary validation workflow files were removed.

[trypsynth]

Merged, thanks! #197 had also translated these 11 strings, with different wording, in strings_backtalk_20261015.xml, which made duplicate resources. I kept your wording from this PR, since it's the newer one, and removed the earlier copies. If you meant the #197 wording instead, just send a PR.

[matejplch626-afk]

Thanks! Keeping the newer wording from #202 is exactly what we intended.