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/howto-ai-automation.html

@@ -31,7 +31,7 @@
             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="../../style.css" />
+        <link rel="stylesheet" href="../../style.css?v=3332fbba93" />
         <style>
             /* Blog post specific overrides — matching homepage light theme */
             body {