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/0030-halkyon-train.md

@@ -1485,7 +1485,12 @@ Strava. What was found, 27 Oct:
   where the device doesn't record (the desktop), which keeps the plans beside the days
   in Profile. The frame is Learn's, moved into halkyon_ui for every app
   (`NavigationFrame`, `TabsStack`): a rail with the app's icon on top from medium
-  windows on, a bar floating above the foot below, a tick on every choice. Driven by
+  windows on, a bar floating above the foot below, a tick on every choice (amended 7 Nov
+  2026, the developer's decision: the bar is flush with the foot, as Material 3 Expressive
+  keeps it, 64 dp in the theme's own colour across the whole width, and a fade 32 dp high
+  into the background of the screen in view above it replaces the floating card, so what
+  scrolls on beneath it fades out rather than being cut off; halkyon_ui's
+  `FlushNavigationBar`, the rail unchanged). Driven by
   go_router as Learn's (a `StatefulShellRoute`, each tab keeping its own stack): a
   workout's page opens in Home and a day's in Profile with the tabs beside them, the
   route and plan editors and the recording over them; over keeping `Navigator.push`
@@ -1607,7 +1612,7 @@ Strava. What was found, 27 Oct:
     expanded windows on, the map and the rest side by side (a 400 px pane, Material's
     supporting pane, as the Maps tab's list and map, D60). Without a track or without
     the map, the rest alone, as before. The page stays in Home (back leads there) but
-    opens on the root navigator, over the shell, so without the floating bar (D60 had
+    opens on the root navigator, over the shell, so without the navigation bar (D60 had
     it run on beneath the bar).
   - **What the map's source sees** ("Map by OpenFreeMap: it sees…", and the link to what
     it keeps) moves behind halkyon_ui's question mark (`HelpButton`, which gained an