Improve sitemap, RSS, and SEO guardrails

docs/seo-guardrails.md

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+# SEO Search Guardrails
+
+These rules protect search discovery and must remain enforced by `scripts/validate_seo.py` in CI.
+
+- `sitemap.xml` and `rss.xml` are XML-only responses. They must not render the shared HTML layout.
+- `sitemap.xml` includes canonical, indexable URLs only. Redirect-only URLs and authenticated routes are excluded.
+- Blog URLs use the post's actual `UpdatedAt` value for `lastmod`; the homepage uses the most recent active FAQ, announcement, or displayed blog update.
+- Sitemap collection must page through every published blog post. Do not introduce a fixed total-content limit.
+- `/rss.xml` is the one canonical feed. `/feed.xml` permanently redirects to it.
+- `robots.txt` declares one canonical sitemap and never blocks XML resources.
+- Canonical URLs always use `https://www.taxbaik.com` and include the current indexable path. Paginated and category-filtered blog pages set an explicit canonical URL.
+
+Run locally with:
+
+```powershell
+python scripts/validate_seo.py
+```