Add theme/font CLI options and mobile Safari keyboard support

- Add --theme, --font-family, --font-size CLI options
- Pass theme/font config via HTML data attributes to frontend
- Add hidden textarea for mobile keyboard input capture
- Handle special keys (Enter, Backspace, arrows, Tab) on mobile
- Focus textarea on touch/click to trigger mobile keyboard

Bump version to 0.5.3

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "textual-webterm"
-version = "0.5.2"
+version = "0.5.3"
 description = "Serve terminal sessions over the web"
 authors = ["Will McGugan <will@textualize.io>"]
 license = "MIT"