fix(v2 ownership): synthesized Person stubs no longer emit schema:url self-loop

Empirical batch 3 (`gabyx/pandoc`, 14 self-loops) showed Bug P still
in the output despite the agent-side fixes shipped in 9aadfa7 +
97285c1. Root cause: `_synthesize_owner_person_stub()` in
`ownership_check.py` (used by `guarantee_repo_author` to recover repos
whose `schema:author` array reconciliation emptied) builds the Person
with `schema:url = profile_url = "https://github.com/{handle}"` — the
same value used as the stub's `id`. By construction every salvaged
stub has the tautological self-loop the agent-side guards were
designed to prevent; the stubs are added downstream of the agents so
the agent fixes can't see them.

Set `schema:url` to `None` for these stubs. The Person's `@id` already
carries the github profile URL; consumers that want it read `@id` or
follow `pulse:githubUsername`. SHACL allows `schema:url` to be null.

Companion observation (not a separate fix here): batch 3 also showed
the previously fixed Bug A membership filter is working — `vita-epfl/social-nce`
correctly dropped the spurious Vita-Brazil / Vita-Germany / Vita-China /
Vita-UK Memberships from a fuzzy-`query_orcid` match against the
`vita-epfl` string. The Organization entities themselves still appear
in the @graph as orphan stubs (the org_agent had already added them
before the membership filter ran). That's the next class to address —
worth doing inside the strategy framework the user proposed (tool
guards / provenance stamps / critic activation) rather than another
inline filter.

Author: caviri

src/v2/pipeline/stages/ownership_check.py

@@ -1067,7 +1067,13 @@ def _synthesize_owner_person_stub(handle: str) -> dict[str, Any]:
         },
         "idSource": "pulse:githubUsername",
         "schema:name": handle,
-        "schema:url": profile_url,
+        # `schema:url` intentionally left None — for github-only synthesized
+        # stubs the only candidate URL would be the github profile, which
+        # IS the Person's `id`. Emitting it produces a tautological
+        # self-loop (Bug P, 1505 cases in the production audit + 14 more
+        # observed in `gabyx/pandoc` even after the agent-side fixes,
+        # because the stubs are added downstream of those agents).
+        "schema:url": None,
         "pulse:githubUsername": handle,
         "pulse:orcidIdentifier": None,
         "pulse:infosciencePersonIdentifier": None,