feat(analytics): add Plausible custom-event markings for six goals

Mark the six conversion goals on the self-hosted Plausible instance so the
events match the goals to be registered in Plausible. Event names verbatim:
Trial, FAQ, Buy, Custom Quote, search posts, Project Plan.

CSS-class markings (work without JS logic, on the clickable element):
- FAQ  -> index/de/es index .faq-card; odoo-hosting-2027 + odoo-community-upgrade
          (de/es twins) and australia <summary>; support.html .faq-question
- Buy  -> index/de/es index .btn-buy anchors; australia + bootcamp native
          post_basket submit buttons (forms stay native POST)

JS call markings in script.js (loaded by index, de/index, es/index):
- Trial        on the successful trial-form POST (.then branch)
- Custom Quote on the successful custom-quote POST (.then branch)
- Project Plan on the successful business-wizard submit
- search posts on the FIRST input of #blogSearch only (guard flag, one per
  pageview, not on every keystroke, not on #ocaSearch)

Nothing fires on page load; the 'Start the free trial' anchors that only
scroll to #trialCard are deliberately not tagged. One goal per topic across
all languages, no language suffix. No visual, behavioural or request change.

script.js

@@ -623,6 +623,7 @@ var si = 0,
                     headers: { 'Content-Type': 'application/json' },
                     body: JSON.stringify(UTM.inject({ email: email, location: location }))
                   }).then(function() {
+                    if (window.plausible) window.plausible('Trial');
                     trialForm.style.display = 'none';
                     document.getElementById('trialSuccess').classList.add('visible');
                   }).catch(function() {
@@ -651,9 +652,14 @@ var si = 0,
                         '<div class="blog-empty">Could not load blog posts.</div>';
                 });
 
+            var blogSearchTracked = false;
             document
                 .getElementById("blogSearch")
                 .addEventListener("input", function () {
+                    if (!blogSearchTracked) {
+                        blogSearchTracked = true;
+                        if (window.plausible) window.plausible('search posts');
+                    }
                     blogState.searchTerm = this.value;
                     blogState.currentPage = 1;
                     renderBlog();
@@ -737,6 +743,7 @@ var si = 0,
                     }).catch(function () { /* ignore */ });
 
                     /* Show success message — we'll email the report */
+                    if (window.plausible) window.plausible('Project Plan');
                     form.style.display = 'none';
                     success.style.display = 'block';
                 });
@@ -898,6 +905,7 @@ var si = 0,
                             }))
                         }).then(function(r) {
                             if (!r.ok) throw new Error('bad status ' + r.status);
+                            if (window.plausible) window.plausible('Custom Quote');
                             customQuoteForm.style.display = 'none';
                             document.getElementById('customQuoteSuccess').style.display = 'block';
                             submitBtn.textContent = 'Submit Request';