fix(bootcamp): Buy forms add the Q1 2027 cohort (product 12 -> 17)

All nine Buy forms on the bootcamp pages (EN/DE/ES, three each) posted
product_id 12, which the shop resolves to 'Bootcamp - Q1-2026-eng'. The
advertised cohort is Q1 2027 (starts Thu 21 Jan 2027), so a customer
buying the 2027 bootcamp received the 2026 cohort. Both are 595.00 and
neither cart was empty, so it went unnoticed; the form's info field reads
'Q1 2027, English' while the product was 2026.

product_id 12 -> 17 in every bootcamp Buy form, all three languages.
The info field is kept (it renders as the cart line description via
sale.order.line.name, so it is read downstream); it is truthful.
static/buy.js doc comment updated to match. Nothing else changed:
plausible-event-name=Buy class, target=_blank form post, prices and
layout untouched.

static/buy.js

@@ -1,7 +1,7 @@
 /* buy.js — page-local checkout helper (progressive enhancement).
  *
  * The checkout itself is a native <form method="post" target="_blank"> that posts
- * basket=[{"product_id":12,"qty":1}] + clear=1 to
+ * basket=[{"product_id":17,"qty":1}] + clear=1 to
  * https://20.odoo4projects.com/shop/post_basket. With JavaScript off it still works.
  *
  * This file only adds attribution: on submit it appends the utm_* hidden inputs