feat: add download data empty state button to keyboard (#627)

[prince-0408]

Description

Closes #627

This PR implements the empty state for Scribe keyboards when the keyboard
has been installed but language data has not yet been downloaded. A blue
"Please download language data" button now appears at the top of the
keyboard, matching the Figma design. Tapping the button opens the Scribe
app and navigates directly to the Download Data screen.

Changes Made

Keyboards/KeyboardsBase/KeyboardViewController.swift

• Added downloadDataBtn (UIButton?) property to hold a reference to
  the empty state button
• Added hasLanguageData() — checks if the language SQLite file exists
  in the shared app group container (group.be.scri.userDefaultsContainer)
• Added showDownloadDataBtn() — creates and lays out the blue CTA button
  pinned to the top of the keyboard view using Auto Layout
• Added conditionallyShowDownloadDataBtn() — shows or hides the button
  based on data availability; only shown in .idle command state, hidden
  during translate / conjugate / plural / displayInformation states
• Added openScribeApp() — uses the UIResponder chain to open the
  scribe:// URL scheme, directing the user to the Scribe app download screen
• Called conditionallyShowDownloadDataBtn() at the end of loadKeys()
  so it re-evaluates on every keyboard load

Keyboards/KeyboardsBase/ScribeFunctionality/CommandVariables.swift

• Added downloadDataMsg variable with default English fallback:
  "Please download language data"

Language Interface Variables (11 keyboards)

Added localized downloadDataMsg to each keyboard's layout function:

Language	Message
English	Please download language data
German	Bitte Sprachdaten herunterladen
French	Veuillez télécharger les données linguistiques
Spanish	Por favor descarga los datos del idioma
Italian	Scarica i dati della lingua
Portuguese	Por favor baixe os dados do idioma
Russian	Загрузите языковые данные
Swedish	Ladda ner språkdata
Norwegian	Last ned språkdata
Hebrew	אנא הורד נתוני שפה
Indonesian	Unduh data bahasa

Scribe/Info.plist

• Registered the scribe:// custom URL scheme (CFBundleURLSchemes) so
  the Scribe app can be opened from the keyboard extension

Scribe/AppDelegate.swift

• Added application(_:open:options:) handler for the scribe:// URL scheme
• Posts the existing NavigateToDownloadScreen notification which
  InstallationVC already listens for and handles by pushing
  DownloadDataScreen

Testing

• Install a Scribe keyboard without downloading data — blue button
  appears at top of keyboard
• Tap the button — Scribe app opens on the Download Data screen
• Download language data in the app — switch back to keyboard,
  button is gone
• Trigger a Scribe command (translate/conjugate/plural) — button
  is hidden during command mode
• Test on all 11 supported languages — localized message appears
  correctly

Notes

• The UIResponder chain URL trick works on a real device. In the
  simulator the button visibility can be tested but the tap-to-open
  behaviour requires a physical device
• RequestsOpenAccess remains false in the keyboard extension —
  the responder chain approach does not require full access

[github-actions]

Thank you for the pull request! 💙

The Scribe-iOS team will do our best to address your contribution as soon as we can. If you're not already a member of our public Matrix community, please consider joining! We'd suggest that you use the Element client as well as Element X for a mobile app, and definitely join the General and iOS rooms once you're in. Also consider attending our bi-weekly Saturday dev syncs. It'd be great to meet you 😊

Note

Scribe uses Conventional Comments in reviews to make sure that communication is as clear as possible.

[github-actions]

Maintainer Checklist

The following is a checklist for maintainers to make sure this process goes as well as possible. Feel free to address the points below yourself in further commits if you realize that actions are needed :)

• Tests for changes have been written and the CI unit test, linting and formatting workflows within the PR checks do not indicate new errors in the files changed

• The CHANGELOG has been updated with a description of the changes for the upcoming release and the corresponding issue (if necessary)

[andrewtavis]

Thanks for this, @prince-0408! Sorry to ask you to do a bunch of reformatting, but then it'll only be done this once :) Can you switch this over to four spaces to match the new style?

[prince-0408]

Done! @andrewtavis
I have now updated my work to match the version of the main branch. I changed everything to use four spaces for indentation. I'm glad I could make things consistent. It's no problem all.