fix(seo-data,seo): backtest on a second, native site — two real bugs

Everything on this branch was grounded on ONE Astro repo. A native PHP site
(lavageangels356.fr) broke two things that looked fine there.

BUG 1 — sitemap counted images as pages. _locs matched
`el.tag.endswith("}loc")`, and <image:loc> from Google's image-sitemap
namespace ALSO ends with '}loc'. Astro's sitemap has no image extension, so
this was invisible. The native site's does: 24 <url> + 3 <image:loc> came back
as count=27. The COVERAGE denominator was 12.5% too high and img/logo.png was
about to be sampled and audited as a page.
Fixed with two locks: walk the DIRECT children of each <url>/<sitemap> instead
of root.iter() (which alone excludes <image:image><image:loc>), and test the
sitemaps.org namespace explicitly. Regression fixture carries the image
extension; the old endswith code returns 9 URLs against it, the new one 7 with
zero images.
Verified both sites: native 27 -> 24, zero images; Astro unchanged at 86.

BUG 2 — the C1c family heuristic was tuned to one URL layout. "First path
segment" works for NESTED city pages (/creation-site-internet/essonne-91/ →
25 pages, 1 family) and FAILS for FLAT ones (/lavage-auto-pomponne,
/lavage-auto-torcy → 8 pages, 8 singletons). Consequence: C1c's rule "sample
>=3 from the largest family" would have targeted /services (5) and missed the
8 city pages entirely — the exact doorway-page risk the 30/70 rule exists to
catch.
Family is now "shared parent path OR shared slug prefix (>=3 URLs sharing 2+
hyphen tokens)", with both real layouts as the worked examples, plus a
sanity-check: a sitemap yielding almost as many families as URLs has defeated
the heuristic, not proved the site has no templates. Fixed in seo-analyzer and
in the geo pointer that referenced it.

Backtest results on the native site for everything else: url-guard accepts the
domain; source-scope excludes only .git (no dist/build/out exists — the
exclusions are correctly no-ops, and cache/ holds only .htaccess+.gitignore so
it is rightly untouched); the sameAs check runs and finds zero (a real GEO gap
for that site, not a tool bug); links are present in the served HTML (PHP is
SSR), so C3 is feasible there.

Verified: seo-data 119 -> 122 pass, 0 fail; full suite green; py_compile clean.

lib/seo-data/fixtures/sitemap.xml

@@ -1,9 +1,19 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
+        xmlns:xhtml="http://www.w3.org/1999/xhtml"
+        xmlns:image="http://www.google.com/schemas/sitemap-image/1.1">
+  <!-- image:loc also ends with }loc — it must NOT be counted as a page -->
   <url>
     <loc>https://ex.com/</loc>
     <changefreq>weekly</changefreq>
     <xhtml:link rel="alternate" hreflang="en" href="https://ex.com/en/" />
+    <image:image>
+      <image:loc>https://ex.com/img/logo.png</image:loc>
+      <image:title>Logo</image:title>
+    </image:image>
+    <image:image>
+      <image:loc>https://ex.com/img/hero.jpeg</image:loc>
+    </image:image>
   </url>
   <url><loc>https://ex.com/services</loc></url>
   <url><loc>https://ex.com/blog</loc></url>