fix(docs): page help buttons open the right topic + wiring guard

The Federation and Runs help buttons opened the architecture doc:
federation.md/runs.md existed as assets but had no _DocEntry, so
showFaiDoc resolved the unknown slug to _kDocs.first. Register both
(onWelcome: false, so they don't clutter the newcomer grid but are
reachable), split the Welcome grid onto the curated subset, and make
the unknown-slug fallback assert in debug instead of silently opening
the wrong topic.

Guard (no-bugfix-without-a-guard): doc_help_wiring_test.dart scans
lib/ for every showFaiDoc('slug') call and asserts each has a
registered entry AND both assets/docs/<slug>[_de].md files. Exposes
kKnownDocSlugs for the test.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_en.arb

@@ -58,6 +58,10 @@
   "welcomeDocFlowsBlurb": "YAML basics, templating reference, the extract→summarize example.",
   "welcomeDocApprovalsTitle": "Approvals",
   "welcomeDocApprovalsBlurb": "Human-in-the-loop checkpoints — when to use them, how the audit log records them.",
+  "welcomeDocFederationTitle": "Federation",
+  "welcomeDocFederationBlurb": "Connect other hubs (satellites) so their capabilities become usable here — what a satellite is and how enrolment works.",
+  "welcomeDocRunsTitle": "Background runs",
+  "welcomeDocRunsBlurb": "Flows that keep working in the background — what they are for, how to switch the feature on and monitor the runs.",
   "helpTooltip": "Help",
   "errApprovalRejected": "Approval rejected by reviewer.",
   "errApprovalRejectedHint": "The reviewer marked this step as rejected. Check the audit log for the reviewer's reason.",
@@ -112,6 +116,7 @@
   "sidebarSettingsTooltip": "Settings (⌘;)",
   "sidebarChannelTooltip": "Active channel — click to switch.\nproduction = stable · beta = pre-release · dev = rolling · local = workspace",
   "buttonCancel": "Cancel",
+  "buttonLearnMore": "Learn more",
   "buttonSave": "Save",
   "buttonClose": "Close",
   "buttonRetry": "Retry",
@@ -1793,6 +1798,8 @@
   },
   "federationAddDialogTitle": "Issue an enrollment token",
   "federationNameLabel": "Satellite name",
+  "federationAddIntro": "A satellite is another hub this hub connects to — its capabilities then become usable here in flows. You give it a name and receive a one-time token the satellite uses to enrol with this hub.",
+  "federationNameHelp": "A free-form name to recognize this satellite in the list (e.g. its location or purpose). Display only — it changes nothing technical.",
   "federationIssueButton": "Issue",
   "federationIssueFailed": "Could not issue token: {error}",
   "@federationIssueFailed": {