infrastructure: make the page member-facing; lighten the light-mode menu-bar stripe

- condense the page to what a member needs: where services run (Infomaniak),
  what backups mean to them, the .coop domain via domains.coop, mail via
  Scaleway, the Matrix space and the accounts they may meet
- drop operator detail (migration narration, DNS record inventory, scheduled-task
  internals, admin-only components, internal account/credential identifiers) to
  co-op/ops-docs; fix a heading glitch where a line began with '#infrastructure'
- brand.css: light-mode .md-tabs uses the header's pale wash #e8f5e8 (was the
  saturated --green-deep) with a warm hairline; dark scheme unchanged

publishing/brand.css

@@ -185,15 +185,21 @@
   font-weight: 600;
 }
 
-/* Tabs and the search field pick up the brand green. */
+/* The menu-bar (tab) strip. In light it is the same pale green WASH as the
+ * header — #e8f5e8, the homepage's "open source" pill — not a saturated fill:
+ * the deep greens are accents (links, active navigation, rules), and a large
+ * --green-deep bar clashed with the rest of the light palette. A warm hairline
+ * separates the wash from the cream page below it. Dark is unchanged. */
 .md-tabs {
-  background-color: var(--green-deep);
+  background-color: #e8f5e8;
+  border-bottom: 1px solid var(--border);
 }
 /* In dark, keep the tab row the same green as the header bar so the text on it
  * clears 4.5:1 against green-mid (green-deep against near-black text is only
  * ~4.2:1 — marginal for the small tab labels). */
 [data-md-color-scheme="slate"] .md-tabs {
   background-color: var(--green-mid);
+  border-bottom: none;
 }
 .md-search__input {
   background-color: rgba(255, 255, 255, 0.92);