fix: compute first changed diff line from patch hunks

Uses hunk contents to find the first modified line instead of the hunk start
Handles added, removed, and binary-only patches more accurately
Adds tests for patch parsing edge cases

packages/ui/src/components/views/DiffView.test.ts

@@ -0,0 +1,26 @@
+import { describe, expect, test } from 'bun:test';
+
+import { getFirstChangedModifiedLineFromPatch } from './diffPatchUtils';
+
+describe('getFirstChangedModifiedLineFromPatch', () => {
+  test('returns the first added line instead of the hunk context start', () => {
+    expect(getFirstChangedModifiedLineFromPatch(`diff --git a/src/file.ts b/src/file.ts
+@@ -56,10 +56,11 @@
+ unchanged 58
+ unchanged 59
+ unchanged 60
++changed 61
+ unchanged 62`)).toBe(59);
+  });
+
+  test('returns the following modified line for deletion-only hunks', () => {
+    expect(getFirstChangedModifiedLineFromPatch(`@@ -10,4 +10,3 @@
+ context
+-removed
+ after`)).toBe(11);
+  });
+
+  test('returns null when the patch has no hunk change lines', () => {
+    expect(getFirstChangedModifiedLineFromPatch('Binary files a/image.png and b/image.png differ')).toBeNull();
+  });
+});