feat: add dark mode support - #222

This PR introduces app-wide dark mode support by switching to a DayNight base theme and migrating many UI surfaces/text to theme-resolved semantic colors, plus adds a user-facing appearance mode setting.

Changes:

• Switch Theme.openCloud to Theme.AppCompat.DayNight.* and introduce semantic color tokens with values-night overrides.
• Replace hardcoded light colors in many layouts/drawables with ?attr/* / ?android:attr/* theme attributes.
• Add an “Appearance” setting backed by an AppearanceMode enum and apply it at app startup via AppCompatDelegate.

• Files reviewed: 59/59 changed files
• Comments generated: 3
• Review effort level: Lite

• Files reviewed: 63/63 changed files
• Comments generated: 1
• Review effort level: Lite

Suppressed comments (9)

opencloudApp/src/main/java/eu/opencloud/android/MainApp.kt:114

• setDefaultNightMode only updates activities managed by an AppCompatDelegate, but WhatsNewActivity is a FragmentActivity (and CopyToClipboardActivity is a framework Activity). With the system set to a different mode, those activities do not receive this user-selected Light/Dark mode. Migrate the remaining framework activities to AppCompat or apply the stored mode/configuration to them explicitly.

        AppCompatDelegate.setDefaultNightMode(appearanceMode.nightMode)

opencloudApp/src/main/java/eu/opencloud/android/presentation/accounts/ManageAccountsDialogFragment.kt:81

• AlertDialog here is still android.app.AlertDialog, so removing the explicit Theme_AppCompat_Dialog_Alert wrapper means this builder does not consume the AppCompat alertDialogTheme configured in Theme.openCloud. The manage-accounts dialog can consequently use platform/light dialog chrome instead of the selected DayNight theme; use the AppCompat builder or retain the wrapper.

        val builder = AlertDialog.Builder(requireContext())

opencloudApp/src/main/java/eu/opencloud/android/presentation/files/filelist/FileListAdapter.kt:276

• This row color is themed, but the PNG branch below still sets the thumbnail background to R.color.background_color (line 313). Transparent PNG thumbnails will therefore retain a white background in dark mode; use the themed surface color for that branch as well.

            holder.itemView.setBackgroundColor(colorSurface)

opencloudApp/src/main/java/eu/opencloud/android/presentation/settings/SettingsFragment.kt:78

• The new tests verify the enum mapping and preference initialization, but none exercises this change listener. A regression here could leave the preference value changing without calling AppCompatDelegate.setDefaultNightMode, so add an instrumentation test that selects LIGHT/DARK and verifies the applied night mode (and persisted value).

            setOnPreferenceChangeListener { preference, newValue ->
                val appearanceMode = AppearanceMode.fromPreferenceValue(newValue as String)
                preference.summary = entries[findIndexOfValue(appearanceMode.name)]
                AppCompatDelegate.setDefaultNightMode(appearanceMode.nightMode)
                true

opencloudApp/src/main/res/drawable/numberkeyboard_key_bg_pressed.xml:4

• The new night pressed background is #31515D, but every keypad label still uses numberkeyboard_key_text_color.xml, whose pressed-state color is the fixed @color/color_accent (#396676). The pressed labels therefore have very low contrast in Dark mode. Make the pressed text color theme-aware and choose a color with sufficient contrast against colorSelection.

    <solid android:color="?attr/colorSelection" />

opencloudApp/src/main/res/layout/edit_share_layout.xml:108

• The two visible sharing switch labels above still hardcode @color/color_accent (lines 63 and 95). In the new DayNight theme they sit on the dark window background, where #396676 has insufficient text contrast; changing only the error label to colorOnSurfaceVariant leaves the primary controls hard to read. Use a light surface text token for these labels or provide a night color.

                android:textColor="?attr/colorOnSurfaceVariant"

opencloudApp/src/main/res/layout/rate_me_dialog.xml:70

• The buttons now use colorOnPrimary, but the same dark-themed dialog still renders its title and description with the unchanged hardcoded @color/color_accent (#396676) at lines 34 and 50. Once the DayNight dialog surface is #1E1E1E, those 20sp/16sp texts have insufficient contrast. Make these dialog text colors use a light semantic surface color or provide a night override as well.
  opencloudApp/src/main/res/layout/remove_files_dialog.xml:14
• This card is now colorSurface in night mode, but its Button.Borderless children still get the shared hardcoded @color/color_accent text color (#396676). On the night surface (#1E1E1E) that is low contrast, so the dialog actions become difficult to read. Make the shared borderless-button text color theme-aware (and update the other custom dialogs that use it).
  opencloudApp/src/main/res/values/styles.xml:101
• Switching the alert dialog to a DayNight parent makes its surface dark, but buttonBarButtonStyle still inherits Widget.AppCompat.Button.Borderless.Colored, whose action text uses colorAccent (#396676). That color has insufficient contrast on the night surface (#1E1E1E), so the positive/negative actions of the many themed alert dialogs become difficult to read. Give the dialog button style a night-aware/light semantic text color instead of relying on the accent.

• Files reviewed: 63/63 changed files
• Comments generated: 4
• Review effort level: Lite