feat: e-ink borders for cards and drawer items

[dalekirkwood]

Summary

Secondary visual refinements for e-ink mode. Stacked on top of jensomato#178 (which targets jensomato/ReadeckApp develop).

When e-ink mode is on:

• Bookmark cards: black border, white background, zero elevation shadow
• Drawer items: black outline on selected items instead of gray background
• Card image crossfade: disabled (avoids ghosting on load)

Implementation

Uses a LocalEInkMode CompositionLocal to avoid threading the boolean through every composable parameter. Provided once at the app root, read wherever needed.

• Theme.kt: val LocalEInkMode = staticCompositionLocalOf<Boolean> { false }
• MainActivity.kt: wraps app in CompositionLocalProvider
• BookmarkCard.kt: conditional border, elevation, container color
• BookmarkListScreen.kt: new EInkAwareNavigationDrawerItem wrapper with border on selected items

Depends on

jensomato#178 must merge first. This branch is based on feat/eink-mode.

Test plan

• Compiles, all tests pass
• Manual: cards have black borders when e-ink mode is on
• Manual: selected drawer items show black outline instead of gray background
• Manual: e-ink mode off looks identical to before