fix(init): preserve welcome banner alignment (#1255)

## Summary

The `sentry init` welcome screen centered every block-art row
independently. Because the top row is narrower than the rest, the arch
shifted to the right relative to the wordmark.

Center the banner using its widest row so the artwork keeps its authored
indentation while the responsive variants remain unchanged. Add an Ink
regression test that verifies every row position and the centered banner
origin.

## Test plan

- [x] `pnpm run lint`
- [x] `pnpm vitest run test/lib/init/ui/ink-app.snapshot.test.tsx
--coverage.enabled=false`
- [x] `pnpm run typecheck`
- [x] `git diff --check`

Author: betegon

src/lib/init/ui/ink-app.tsx

@@ -625,13 +625,15 @@ function IntroScreen({
     bannerRows.length === 0 || bannerLinesWidth(bannerRows) <= bodyWidth
       ? bannerRows
       : bannerLinesForWidth(bodyWidth);
+  // Center the banner as one unit; centering rows separately shifts shorter rows.
+  const bannerWidth = bannerLinesWidth(banner);
 
   return (
     <Box alignItems="center" flexDirection="column" width={bodyWidth}>
       <Box
-        alignItems="center"
         flexDirection="column"
         marginBottom={welcomePrompt ? 2 : 1}
+        width={bannerWidth}
       >
         {banner.map((row, i) => (
           // biome-ignore lint/suspicious/noArrayIndexKey: positional banner rows

test/lib/init/ui/ink-app.snapshot.test.tsx

@@ -14,6 +14,10 @@ import { setTimeout as sleep } from "node:timers/promises";
 import { render } from "ink";
 import { createElement } from "react";
 import { describe, expect, test } from "vitest";
+import {
+  bannerLinesWidth,
+  FULL_BANNER_LINES,
+} from "../../../../src/lib/banner.js";
 import {
   App,
   formatFeedbackBanner,
@@ -307,6 +311,31 @@ describe("Ink App snapshot", () => {
     expect(hasForcedWhiteForeground(withoutFeedbackBanner(frame))).toBe(false);
   });
 
+  test("welcome banner preserves row alignment while centering the art", async () => {
+    const store = new WizardStore({ bannerRows: FULL_BANNER_LINES });
+    setWelcomePrompt(store);
+
+    const terminalColumns = 120;
+    const frame = stripAnsi(
+      (await renderApp(store, terminalColumns)).allOutput()
+    );
+    const lines = frame.split(LINE_SPLIT_RE);
+    const bannerOrigin = Math.floor(
+      (terminalColumns - bannerLinesWidth(FULL_BANNER_LINES)) / 2
+    );
+
+    for (const { content } of FULL_BANNER_LINES) {
+      const visibleContent = content.trimStart();
+      const leadingSpaces = content.length - visibleContent.length;
+      const renderedRow = lines.find((line) => line.includes(visibleContent));
+
+      expect(renderedRow).toBeDefined();
+      expect(renderedRow?.indexOf(visibleContent)).toBe(
+        bannerOrigin + leadingSpaces
+      );
+    }
+  });
+
   test("intro banner shrinks to fit narrow terminals (never wraps)", async () => {
     // A banner wider than the narrow terminal; distinctive marker so we can tell
     // whether it was rendered verbatim or replaced by a fitting variant.