fix: make icon/folder rename dialog follow system light/dark theme

[MiMoHo]

Type of change(s)

• Bug fix

What changed and why

The folder/icon rename dialog showed dark text on a dark background in light system mode (dark mode was fine), making it unreadable.

Root cause is a dialog surface/text-color mismatch, not a hardcoded text color:

• MainActivity (which opens the rename dialog) is declared with android:theme="@style/LauncherTheme", whose parent is Theme.Material3.Dark.NoActionBar — a forced-dark theme so the launcher can draw a transparent window over the wallpaper. MainActivity.onCreate also sets useDynamicTheme = false, so BaseSimpleActivity never calls setTheme(getThemeId(...)) to switch to a light theme. The activity theme is therefore dark regardless of system mode.
• On Android 12+ isDynamicTheme() defaults to true, so commons' getAlertDialogBuilder() returns MaterialAlertDialogBuilder(activity), inheriting that forced-dark context. LauncherTheme does not define materialAlertDialogTheme/colorSurface, so the dialog surface stays the default Material3 dark surface even in light mode.
• The dialog text uses getProperTextColor() (you_neutral_text_color), which is dark in day / light in night. Light mode therefore renders dark text on a dark surface = unreadable; dark mode renders light text on dark = fine.

Fix: in the dynamic-theme path, build the dialog from a ContextThemeWrapper carrying the proper day/night theme (activity.getThemeId()), so the Material dialog surface follows the system light/dark mode. This mirrors the precedent MainActivity already uses for its popup menu (ContextThemeWrapper(this, getPopupMenuTheme())). getThemeId() resolves to AppTheme.Base.System.Light in light mode / AppTheme.Base.System in dark mode, both of which set materialAlertDialogTheme and colorSurface=you_dialog_background_color (day/night). The non-dynamic path is left byte-for-byte identical (it already sets an explicit window background and renders correctly). MaterialAlertDialogBuilder subclasses androidx.appcompat.app.AlertDialog.Builder, so setupDialogStuff(view, this, ...) still type-checks.

Tests performed

Built the fossDebug variant and verified on an Android 15 (API 35) emulator:

Set Fossify as home app; forced light mode; long-pressed Phone icon -> Rename. Dialog shows light surface with dark readable 'Phone' text (fixed). Forced dark mode, reopened Rename -> dark surface with light readable text (not regressed).

Also confirmed detekt, lint, unit tests and the build all pass locally (CI-equivalent).

Closes the following issue(s)

• Closes Folder rename dialog: Dark text on dark background #198

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator.
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.

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