feat(ui): large-screen layout - adaptive nav, content max-width, unlock rotation

[SiteRelEnby]

Large-screen / tablet support at the app-root chrome level (part of #65). Two related changes, both in SheafApp.

1. Adaptive top-level navigation

Swaps the fixed bottom NavigationBar for Material3's NavigationSuiteScaffold, which adapts the top-level chrome to the window width:

• Compact width (phones): bottom navigation bar, exactly as today.
• Medium/expanded width (tablets, landscape, foldables, large/free-form windows): a navigation rail down the side.
• Non-top-level screens (detail/editor/full-screen): no nav chrome (NavigationSuiteType.None), same as before.

Breakpoint is the standard 600dp compact/medium split, read from the window width so it reacts live to resize / multi-window. Destinations, selection state, and back-stack-preserving navigation are unchanged; only the container drawing them changed.

New dependency: androidx.compose.material3:material3-adaptive-navigation-suite, pinned to the material3 version (1.5.0-alpha17).

2. Content max-width on wide windows

Wraps the NavHost content so a single pane doesn't stretch across a whole tablet: capped at 840dp and centred, with gutters beyond that. widthIn is a no-op below the cap, so phones and split-screen are untouched. The relationship graph opts out (FULL_BLEED_ROUTES) because the pan/zoom canvas wants the whole area.

3. Drop the portrait orientation lock

MainActivity was locked to portrait, so on a landscape tablet or foldable the system pillar-boxed the whole window - black bars either side of the app, including the rail. Removing the lock lets the app fill the window and rotate; the adaptive nav + content cap above handle the resulting widths. Android 16 forces this on large screens once we bump targetSdk, so it's on the path anyway.

Follow-ups (not here)

• Two-pane list/detail on expanded width (members, history) via ListDetailPaneScaffold, and/or a multi-column card grid on Home - the real way to use the extra landscape width rather than leaving gutters.

Testing

:app:assemblePlayRelease :app:testPlayReleaseUnitTest green. Device checklist:

• Phone: bottom bar unchanged; all five tabs and detail screens navigate as before
• Tablet / large window: top-level tabs show as a side rail; content is centred rather than edge-to-edge
• Relationship graph still uses the full width on a tablet
• Resize / unfold across the 600dp line swaps bar <-> rail without losing the current tab
• Rotate a phone / tablet to landscape: app fills the screen, no black pillar-box bars