fix(paint): continuous backgroundColor across wrapped text lines

- Wrap each text line with applyChalk(bgProps) after wrapText so
  background color is reapplied on every wrapped line (wrap-ansi
  doesn't carry ANSI state across line breaks)
- Add wrapped-text backgroundColor regression test
- Fix typo: color=" cyan" → color="cyan" in example
- Add FORCE_COLOR=3 debugging tip to AGENTS.md

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

packages/runtime-tests/integration/components/background-color.test.tsx

@@ -45,3 +45,19 @@ test("child Text inherits backgroundColor from parent Box", async () => {
   expect(raw).toContain("hello");
   expect(raw).toContain(BG_BLUE);
 });
+
+test("wrapped text preserves backgroundColor on every line", async () => {
+  const { frames } = await render(
+    () => (
+      <Box backgroundColor="blue" borderStyle="single" width={10} height={4}>
+        <Text>long text here</Text>
+      </Box>
+    ),
+    { columns: 20 },
+  );
+  const raw = frames.at(-1)!;
+  const lines = raw.split("\n").filter(Boolean);
+  for (const line of lines) {
+    expect(line).toContain(BG_BLUE);
+  }
+});