feat(app): add themeable diff stat colors and soften tooltip border

Add diffAddition/diffDeletion semantic tokens with separate light
(muted green-700/red-700) and dark (bright green-400/red-500) sets,
spread into themes so individual variants can override. Update all
diff stat consumers to use the new tokens.

Soften tooltip border to match dropdown menu styling (thinner border,
accent color, medium shadow).

packages/app/src/components/git-diff-pane.tsx

@@ -1724,7 +1724,7 @@ const styles = StyleSheet.create((theme) => ({
   newBadgeText: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.green[400],
+    color: theme.colors.diffAddition,
   },
   deletedBadge: {
     backgroundColor: "rgba(248, 81, 73, 0.2)",
@@ -1736,17 +1736,17 @@ const styles = StyleSheet.create((theme) => ({
   deletedBadgeText: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.red[500],
+    color: theme.colors.diffDeletion,
   },
   additions: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.green[400],
+    color: theme.colors.diffAddition,
   },
   deletions: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.red[500],
+    color: theme.colors.diffDeletion,
   },
   diffContent: {
     borderTopWidth: theme.borderWidth[1],
@@ -1824,10 +1824,10 @@ const styles = StyleSheet.create((theme) => ({
     userSelect: "none",
   },
   addLineNumberText: {
-    color: theme.colors.palette.green[400],
+    color: theme.colors.diffAddition,
   },
   removeLineNumberText: {
-    color: theme.colors.palette.red[500],
+    color: theme.colors.diffDeletion,
   },
   diffLineText: {
     flex: 1,

packages/app/src/components/sidebar-workspace-list.tsx

@@ -2241,12 +2241,12 @@ const styles = StyleSheet.create((theme) => ({
   diffStatAdditions: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.green[400],
+    color: theme.colors.diffAddition,
   },
   diffStatDeletions: {
     fontSize: theme.fontSize.xs,
     fontWeight: theme.fontWeight.normal,
-    color: theme.colors.palette.red[500],
+    color: theme.colors.diffDeletion,
   },
   kebabButton: {
     padding: 2,

packages/app/src/components/ui/tooltip.tsx

@@ -551,9 +551,9 @@ const styles = StyleSheet.create((theme) => ({
     paddingHorizontal: theme.spacing[2],
     borderRadius: theme.borderRadius.xl,
     backgroundColor: theme.colors.popover,
-    borderWidth: theme.borderWidth[2],
-    borderColor: theme.colors.border,
-    ...theme.shadow.sm,
+    borderWidth: theme.borderWidth[1],
+    borderColor: theme.colors.borderAccent,
+    ...theme.shadow.md,
     zIndex: 1000,
   },
 }));