fix(docs): keep the translated locale trees out of the search index (#662)

Search Console flagged four reasons on 2026-07-28: soft 404, both
duplicate-canonical variants, and noindex. All four sat on
docs.snapotter.com; the landing site was clean.

The cause was boilerplate dominance rather than a broken tag.
/tools/video/crop-video carries 1.3 KB of unique body against 3.5 KB of
identical chrome (nav, sidebar, 21-language switcher), so unrelated tool
docs measured 52-60% full-page similarity. Across 20 locales that was
3,640 of 3,822 submitted URLs. Google read the lot as one duplicate
cluster and began electing arbitrary representatives: /changelog became
the canonical for /tools/image/favicon, and /uk/guide/getting-started for
/nl/tools/image/resize. English tool docs indexed 2 of 10 and localized 4
of 10, while the landing page for those same five tools indexed 5 of 5.

Translated pages now emit `noindex, follow` with a self-canonical, and
sitemap.transformItems drops them from the sitemap. Self-canonical rather
than pointing at English, since noindex paired with a cross-canonical
sends two conflicting instructions. hreflang is removed outright: the
annotation only means something between pages that can all be indexed.

Readers see no change. The language switcher and every in-page link
behave exactly as before.

Verified against a real build: sitemap 3,822 to 182 URLs with zero
translated entries, all 3,640 translated files carrying the noindex and
no English file doing so, docs e2e 100 passed.

tests/unit/surface-playwright-harness.test.ts

@@ -267,7 +267,7 @@ test("docs Playwright collection includes explicit Axe coverage", () => {
   for (const pageName of ["homepage", "getting started", "configuration", "REST API"]) {
     expect(output).toContain(`${pageName} has no Axe violations`);
   }
-  expect(output).toContain("Total: 99 tests in 7 files");
+  expect(output).toContain("Total: 100 tests in 7 files");
 });
 
 test("Turbo passes surface harness overrides through task boundaries", () => {