tasks: consolidate add affordance into a setting (FAB or bottom bar)

Removes the doubled add idiom (top inline-add bar + FAB). A new "Bottom quick-add bar" setting (default off) picks one affordance per screen: off keeps the floating New task button everywhere; on shows a quick-add field pinned to the bottom of a real list (smart lists keep the button, as they have no single target list).

The bottom field floats on the brightest container tone with a shadow so it stands off the task cards, rides above the keyboard (ime ∪ navigation-bar insets), and drops focus when the IME hides so no stray cursor lingers.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/res/values/strings.xml

@@ -198,6 +198,8 @@
     <string name="settings_default_list_first">First available list</string>
     <string name="settings_add_subtask_row">Show \"add a subtask\" row</string>
     <string name="settings_add_subtask_row_hint">An add field at the end of an expanded task\'s subtasks</string>
+    <string name="settings_bottom_add_bar">Bottom quick-add bar</string>
+    <string name="settings_bottom_add_bar_hint">Add tasks from a bar pinned to the bottom of a list, instead of the floating button</string>
 
     <!-- Reminder lead times (custom amounts) -->
     <plurals name="reminder_minutes">