feat(analytics): Plausible snippet on every page, FAQ marked on the bootcamp

The snippet was on 10 of 40 pages, so the Trial / FAQ / Buy / Custom Quote /
search posts / Project Plan goals were inert everywhere else. It now sits
verbatim, in the same <head> position as index.html, on all 39 visitor-facing
pages. email/trial-confirmation.html is deliberately left out (email template).

FAQ: the five <details class="bc-faq"> <summary> elements on the bootcamp page
and its DE/ES twins now carry plausible-event-name=FAQ, and the 15
.faq-question buttons on de/es/support.html get the marking they were believed
to already have. No goal renamed: one FAQ goal across all languages.

No markup, copy or behaviour change, and no third-party request beyond the
snippet itself. verify-html.py PROBLEMS 0; check-links.py OK; event checker
59 PASS / 0 FAIL; impeccable detector +0/-0 findings on the changed files.

odoo/upsell.html

@@ -202,6 +202,12 @@
                 user-select: all;
             }
         </style>
+  <!-- Privacy-friendly analytics by Plausible -->
+<script async src="https://plausible.office.odoo4projects.com/js/pa-NhA7Rf-79VopXFQXhSS4e.js"></script>
+<script>
+  window.plausible=window.plausible||function(){(plausible.q=plausible.q||[]).push(arguments)},plausible.init=plausible.init||function(i){plausible.o=i||{}};
+  plausible.init()
+</script>
     </head>
     <body>
         <div class="page-subtitle">