refactor(app): App-per-screen navigation, remove menu_level entirely

Splits the ad-hoc menu_level state machine into standalone Apps with a
uniform parent/child exit convention (long-press CONFIRM -> parent):
clock_app renamed to home_app (boot-default), new set_clock_app
extracted from home_app's time-edit mode, new ipc_bind_app extracted
from menu_app's old level-2 screen, and the sensor-type selection step
merged into pair_app as its new initial state. menu_app now only holds
the 4-item top-level list (language toggle inline). Also makes both
menu_app and pair_app's up/down navigation cyclic (wraps at both ends).

wristband.uvproj

@@ -375,9 +375,14 @@
               <FilePath>.\App\clock.c</FilePath>
             </File>
             <File>
-              <FileName>app_clock.c</FileName>
+              <FileName>app_home.c</FileName>
               <FileType>1</FileType>
-              <FilePath>.\App\app_clock.c</FilePath>
+              <FilePath>.\App\app_home.c</FilePath>
+            </File>
+            <File>
+              <FileName>app_set_clock.c</FileName>
+              <FileType>1</FileType>
+              <FilePath>.\App\app_set_clock.c</FilePath>
             </File>
             <File>
               <FileName>app_menu.c</FileName>
@@ -389,6 +394,11 @@
               <FileType>1</FileType>
               <FilePath>.\App\app_pair.c</FilePath>
             </File>
+            <File>
+              <FileName>app_ipc_bind.c</FileName>
+              <FileType>1</FileType>
+              <FilePath>.\App\app_ipc_bind.c</FilePath>
+            </File>
             <File>
               <FileName>app_alarm.c</FileName>
               <FileType>1</FileType>