fix(feed): breathing room around divider + FAB back to right/bottom corner

- PostSeparator was a bare 1px line flush against both neighbouring
  cards, so the seam looked like card contact instead of a real
  break. Wrapped it in a 12px vertical padding — now there's 12px
  blank above the line, 1px line, 12px blank below. Trimmed the
  card's own paddingVertical back down since the separator now owns
  the inter-post breathing room.
- FAB was lifted to bottom: max(insets.bottom, 8) + 70 in the previous
  commit which put it far too high (a leftover from the original
  experiment with the absoluteFill wrapper). User wants 12px above
  the NavBar and 12px from the right edge. The Feed screen's
  container ends at the NavBar top (enforced by (app)/_layout.tsx's
  outer <View flex:1> + NavBar sibling), so a simple `right: 12,
  bottom: 12` on position:absolute lands the button exactly there on
  every device. Removed the now-unnecessary absoluteFill wrapper too.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

client-app/app/(app)/feed/index.tsx

@@ -251,43 +251,29 @@ export default function FeedScreen() {
         contentContainerStyle={posts.length === 0 ? { flexGrow: 1 } : undefined}
       />
 
-      {/* Floating compose button.
-       *
-       * Wrapped in a StyleSheet.absoluteFill container with pointerEvents
-       * "box-none" so only the FAB captures touches — taps anywhere else
-       * pass through to the FlatList below.
-       *
-       * Inside the wrapper, alignSelf: 'flex-end' pins to the right;
-       * bottom inset leaves ~14px clearance above the NavBar (≈56px tall
-       * + safe-area-bottom). Explicit `right: 14` is belt-and-braces
-       * for RTL / platform quirks where alignSelf alone might not pin. */}
-      <View
-        pointerEvents="box-none"
-        style={{
+      {/* Floating compose button — pinned 12px from the right edge of
+          the screen and 12px above the NavBar top. The Feed screen's
+          container ends at the NavBar top (see (app)/_layout.tsx), so
+          a plain bottom: 12 measures from exactly that edge. */}
+      <Pressable
+        onPress={() => router.push('/(app)/compose' as never)}
+        style={({ pressed }) => ({
           position: 'absolute',
-          left: 0, right: 0, top: 0, bottom: 0,
-        }}
+          right: 12,
+          bottom: 12,
+          width: 56, height: 56,
+          borderRadius: 28,
+          backgroundColor: pressed ? '#1a8cd8' : '#1d9bf0',
+          alignItems: 'center', justifyContent: 'center',
+          shadowColor: '#000',
+          shadowOffset: { width: 0, height: 4 },
+          shadowOpacity: 0.5,
+          shadowRadius: 6,
+          elevation: 8,
+        })}
       >
-        <Pressable
-          onPress={() => router.push('/(app)/compose' as never)}
-          style={({ pressed }) => ({
-            position: 'absolute',
-            right: 14,
-            bottom: Math.max(insets.bottom, 8) + 70,
-            width: 56, height: 56,
-            borderRadius: 28,
-            backgroundColor: pressed ? '#1a8cd8' : '#1d9bf0',
-            alignItems: 'center', justifyContent: 'center',
-            shadowColor: '#000',
-            shadowOffset: { width: 0, height: 4 },
-            shadowOpacity: 0.5,
-            shadowRadius: 6,
-            elevation: 8,
-          })}
-        >
-          <Ionicons name="create-outline" size={24} color="#ffffff" />
-        </Pressable>
-      </View>
+        <Ionicons name="create-outline" size={24} color="#ffffff" />
+      </Pressable>
     </View>
   );
 }