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-custom-module.html

@@ -36,7 +36,7 @@
             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>
             :root {
                 --primary: #714b67;
@@ -277,6 +277,6 @@
             </div>
         </div>
         </main>
-        <script defer src="/static/agent-odoo4projects/agent.js"></script>
+        <script defer src="/static/agent-odoo4projects/agent.js?v=c3bb0cee2b"></script>
     </body>
 </html>