Support transparent status bar on iOS

[kgarner7]

This is a small change to HTML to make the status bar on iOS transparent. It isn't really notable with the default themes, but is helpful for PWA when using custom CSS. Docs from Apple regarding these tags

• I have tested my changes
• I read this document: https://miniflux.app/faq.html#pull-request

[fguillot]

The text overlap with a transparent status bar, and from my point of view it's harder to read.

Without your changes:

With your changes:

[kgarner7]

Ugh, yeah that looks bad (it looked better on a larger device). Sorry about that .-.
Probably the correct way to do this would be to add another column to user that sets the theme-color, as this is the only way to have the same status bar while not having bad transparency (I wish you could just CSS it, but alas). I'm comfortable actually making these code changes (aside from localization unfortunately), but want to ask, is this actually worthwhile?

[woj-tek]

The text overlap with a transparent status bar, and from my point of view it's harder to read.

Somewhat OT, but on Android with PWA via firefox and white theme status icons are completely not visible (they are white and the header is gone thus white background from Miniflux is used). Should this be considered a bug?