fix(app): tighten the mobile gap under composer track pills

The pill bar floats at the foot of the stream section and the composer has
no top padding, so the bar's paddingBottom is the entire pill-to-composer
gap. Desktop was tuned down to 10 earlier; compact kept the original 16 and
read as a hole on phone. Drop it to 8.

Same constant paddings the import pill row, which tightens with it.

packages/app/src/composer/pill-styles.ts

@@ -2,7 +2,7 @@ import { StyleSheet } from "react-native-unistyles";
 import { SPACING } from "@/styles/theme";
 
 export const COMPOSER_PILL_CLEARANCE = {
-  compact: SPACING[4],
+  compact: SPACING[2],
   wide: 10,
 } as const;
 export const COMPOSER_PILL_MIN_HEIGHT = 32;

packages/app/src/composer/tracks.test.tsx

@@ -103,7 +103,7 @@ describe("ComposerTrackBar", () => {
       right: 0,
       bottom: 0,
       paddingHorizontal: 16,
-      paddingBottom: { xs: 16, md: 10 },
+      paddingBottom: { xs: 8, md: 10 },
     });
     expect(style).not.toHaveProperty("backgroundColor");
     expect(container.firstElementChild?.getAttribute("data-has-layout-handler")).toBe("false");
@@ -122,10 +122,10 @@ describe("ComposerTrackBar", () => {
       borderRadius: 16,
     });
     expect(composerPillStyles.label).toMatchObject({ fontSize: 12 });
-    expect(resolveComposerPillClearance(true)).toBe(16);
+    expect(resolveComposerPillClearance(true)).toBe(8);
     expect(resolveComposerPillClearance(false)).toBe(10);
-    expect(resolveComposerTrackTailClearance(true)).toBe(64);
+    expect(resolveComposerTrackTailClearance(true)).toBe(48);
     expect(resolveComposerTrackTailClearance(false)).toBe(52);
-    expect(COMPOSER_PILL_CLEARANCE).toEqual({ compact: 16, wide: 10 });
+    expect(COMPOSER_PILL_CLEARANCE).toEqual({ compact: 8, wide: 10 });
   });
 });