fix(family): the owed task is tagged by the matching System only, and the ground fixtures build without duplicate keys (#4990)

assess_family_adoption took system_ids for the task it files, which made
the family tool module look like a System-tagging door and tripped the
parity registry. It is not one: the owed task is tagged to the project's
System matching the idea's canonical area, and update_task retags it.
The unit test for each conflict ground passed evidence/conditions twice.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_family_adoption.py

@@ -62,7 +62,7 @@ GOOD = {
 
 @pytest.mark.parametrize("ground", CONFLICT_KEYS)
 def test_each_ground_holds_when_its_needs_are_met(ground):
-    kw = dict(evidence=None, conditions=None, **{**GOOD[ground]})
+    kw = {"evidence": None, "conditions": None, **GOOD[ground]}
     assert conflict_problems(ground=ground, grounds_checked=_checked(ground),
                              fold="their reasoning", **kw) == []