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.

odoo-erp-automation-bootcamp/index.html

@@ -587,7 +587,7 @@
           <form method="post" action="https://20.odoo4projects.com/shop/post_basket" target="_blank">
             <input type="hidden" name="basket" value='[{"product_id":12,"qty":1}]' />
             <input type="hidden" name="clear" value="1" />
-            <button type="submit" class="btn btn-brass btn-lg">Buy for 465.00 USD</button>
+            <button type="submit" class="btn btn-brass btn-lg plausible-event-name=Buy">Buy for 465.00 USD</button>
           </form>
         </div>
       </div>
@@ -610,7 +610,7 @@
           <form method="post" action="https://20.odoo4projects.com/shop/post_basket" target="_blank">
             <input type="hidden" name="basket" value='[{"product_id":12,"qty":1}]' />
             <input type="hidden" name="clear" value="1" />
-            <button type="submit" class="btn btn-brass btn-lg">Buy for 465.00 USD</button>
+            <button type="submit" class="btn btn-brass btn-lg plausible-event-name=Buy">Buy for 465.00 USD</button>
           </form>
         </div>
       </div>
@@ -783,7 +783,7 @@
           <form method="post" action="https://20.odoo4projects.com/shop/post_basket" target="_blank">
             <input type="hidden" name="basket" value='[{"product_id":12,"qty":1}]' />
             <input type="hidden" name="clear" value="1" />
-            <button type="submit" class="btn btn-brass btn-lg">Buy for 465.00 USD</button>
+            <button type="submit" class="btn btn-brass btn-lg plausible-event-name=Buy">Buy for 465.00 USD</button>
           </form>
         </div>
         <ul class="bc-related">