cache-bust local assets; narrow the language facet to scores >= 3

Part 1 — asset versioning: every local <script src> and <link rel=stylesheet> on the
tracked pages now carries ?v=<sha256-of-the-file> (10 hex), computed at BUILD time from
the file's bytes by work/build-asset-versions.py — never hand-typed, and idempotent
(re-running with no file change rewrites nothing). This is what makes an edited
focus-rule.js / photo-upload.js a new URL instead of a stale cache hit.

Part 2 — language facet: a language now counts for the Language filter only when its
0-5 self-assessment is >= LANG_FACET_MIN (3 = 'works in it'). The constant sits beside
the 15-point rule in the page script and its mirror in build-directory.py. Nothing
stored changes; the card's languages chart still prints every language above 0, the
search box is unchanged, and the facet stays an exact membership test against the
card's value. A '1' language no longer offers the person under that language.

blog/posts/from-a-spreadsheet-to-a-running-erp.html

@@ -16,7 +16,7 @@
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&family=Inter+Tight:wght@500;600;700;800&display=swap" rel="stylesheet" />
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" />
-    <link rel="stylesheet" href="../../style.css" />
+    <link rel="stylesheet" href="../../style.css?v=3332fbba93" />
     <style>
       body { background: #0d1b2e; }
       .blog-post { max-width: 720px; margin: 0 auto; padding: 3rem 1.5rem 6rem; color: #171c26; background: #faf7f1; min-height: 100vh; }