feat(learn,todo,train,meditate,ui): the navigation bar flush with the foot, a fade above it

Below medium windows the frame's bar is Material 3 Expressive's again,
flush with the window's foot (decided 7 Nov 2026 by the developer): the
theme's NavigationBar across the whole width, 64 dp in its own colour,
running on beneath the system's bar as Material's does. Right above it a
fade 32 dp high, from the background of the screen in view (the
ScreenTint's, the theme's surface before a screen claims one) made
see-through to that background, so what scrolls on beneath the bar fades
out rather than being cut off; taps pass through it. The rail of wider
windows stays as it was.

halkyon_ui's FloatingNavigationBar becomes FlushNavigationBar, its side
margin, lift and rounded card gone. Its coverOf is now the whole room
content leaves at its end, the system's bar included (the body's bottom
padding: bar, fade and system's bar inside the frame, the system's bar
alone outside it), and floating buttons rise by buttonLiftOf, the same
without the system's bar, which a Scaffold keeps them clear of itself.
Lists, Todo's hour grid and the Plan's sheet keep using coverOf; the
Profile's list no longer adds the system's bar a second time.

Whats-New: The navigation bar sits at the bottom edge again, with a soft fade above it.
Whats-New-De: Die Navigationsleiste sitzt wieder am unteren Rand, mit einem sanften Übergang darüber.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

docs/adr/0033-halkyon-todo.md

@@ -48,7 +48,8 @@ the rail, a wash of strawberry, settings grouped as theirs. What the screenshots
 
 - **D1 Todo's frame is Train's (ADR 0030, D60)**: go_router with a `StatefulShellRoute`,
   every tab keeping its own stack; halkyon_ui's `NavigationFrame`, a bar floating above the
-  foot below medium windows and a rail with Todo's icon on top from medium on, a tick on
+  foot below medium windows (flush with it, a fade above it, since 7 Nov 2026: ADR 0030,
+  D60's amendment) and a rail with Todo's icon on top from medium on, a tick on
   every choice; Todo's account sheet goes. Over a frame of Todo's own, which would make the
   three apps behave differently on the same window.
 - **D2 Four tabs: Today, Upcoming, Inbox, Browse** (recommended, over Todoist's five and over
@@ -553,7 +554,7 @@ The developer's review of 4 Nov 2026, again beside Todoist's screens.
   hidden as the person last left it, remembered with the settings (`TodayView.plan`,
   open at first); **on a phone, a sheet over the day's foot** (the developer's choice,
   over the Plan on wide windows alone and over a strip of tasks above the day), half
-  the body high above the floating bar, closed until asked and while the app runs;
+  the body high above the navigation bar, closed until asked and while the app runs;
   a row held there **lowers the sheet to its heading**, the day free behind it, and it
   rises again once the row is dropped. The sheet is part of Today's screen, not a
   modal route (agent's choice): a modal sheet's barrier would take the drop meant for