feat(bf): fire the trial conversion behind the same consent gate

Adds the second Google Ads label to /odoo-black-friday/: the free-trial
form (#trialForm) now fires AW-18065522009/AtAPCIjjvrAdENn6p6ZD (action
7886320008 "Registrierung") when it is submitted.

Reuses the existing gate in static/ads-consent.js rather than a second
mechanism: the label is read from the page (data-ads-trial-send-to on
#adsConsent), so the script stays generic. The page hands the gate its
real submit function via window.o4pAds.trialConversion; the gate fires
the conversion and runs the submit from the event callback, with the same
700 ms hard timeout that runs it anyway. Nothing fires and no cookie is
set before consent (identical default-deny gate).

The buy conversion is untouched (comments only).

odoo-black-friday/index.html

@@ -1063,7 +1063,9 @@
 
     <!-- Google Ads consent banner — default DENY. The tag loads only after "Accept".
          Markup lives in the page; JS (static/ads-consent.js) reveals it and drives it.
-         With JavaScript off it stays hidden and the native buy forms submit untouched.
+         Two conversions are wired here: the buy forms (data-ads-send-to) and the free-trial
+         form (data-ads-trial-send-to). With JavaScript off it stays hidden and both actions
+         (the native buy POSTs, the trial's own submit) run untouched.
          See wiki/concepts/conversion-tracking-contract. -->
     <div
       id="adsConsent"
@@ -1072,6 +1074,7 @@
       aria-label="Advertising cookie consent"
       data-ads-id="AW-18065522009"
       data-ads-send-to="AW-18065522009/vnDUCPDxt7AdENn6p6ZD"
+      data-ads-trial-send-to="AW-18065522009/AtAPCIjjvrAdENn6p6ZD"
       hidden
     >
       <div class="ads-consent-inner">