docs(register): add ki-produktivitetsmodell as shared-asset

Reported unregistered by ki-leadership (REPO-UNREGISTERED SKIP). Verified
directly against the forge clone rather than trusting the report: no code,
no build chain, no install form — README + CHANGELOG + LICENSE (CC BY 4.0) +
a standalone HTML rendering + a PDF. Matches the other shared-asset entries
(playground-design-system, portfolio-optimiser-commons, llm-security-commons)
far better than standalone, which would demand a false `## Install` heading.

--refresh confirms this was the only drift: 22 registered, 23 on the forge,
exactly this one name missing.

First finding set against the clone: HEADING-MISSING (no `## Non-goals`),
README-H1 and README-LANGUAGE WARNs (title/locale — both operator calls per
this register's own convention, left unset here), and two real LINK-FILE-URL
ERRORs in CLAUDE.md that are not placeholders. That repo's own findings to
fix, not ours.

register/repos.json

@@ -32,6 +32,7 @@
     "playground-design-system": "shared-asset",
     "portfolio-optimiser-commons": "shared-asset",
     "llm-security-commons": "shared-asset",
+    "ki-produktivitetsmodell": "shared-asset",
     ".profile": "org-profile",
     "portfolio-optimiser": "standalone",
     "portfolio-optimiser-claude": "standalone",