feat(incremental): wire maintained tier behind views; rebuild fallback (WP-0011 T4)

Route InformationSpace.all_pages through a maintained UnionIndex: equivalence is
served from the incrementally maintained index (curator bindings re-synced live
from the log fold + detected content edges), exposed in decision-log string form
so results are a behaviour-preserving superset. The index is built lazily and
rebuilt (bounded fallback) when the union mutates (attach/edit invalidate it);
reindex() forces a rebuild and verify_index() runs the I-2 self-healing checker.
all_pages() gains an optional equivalence_groups source (default = fold) so
direct callers are unaffected. SCOPE updated; WP-0011 done. 173 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/shard_wiki/incremental/equivalence.py

@@ -134,6 +134,10 @@ class EquivalenceIndex:
     def unbind(self, a: Identity, b: Identity) -> None:
         self._curator_edges.discard(_pair(a, b))
 
+    def set_curator_edges(self, edges: Iterable[tuple[Identity, Identity]]) -> None:
+        """Replace all curator edges at once (re-syncing from the decision-log fold)."""
+        self._curator_edges = {_pair(a, b) for a, b in edges if a != b}
+
     # -- queries -------------------------------------------------------------
 
     def identities(self) -> frozenset[Identity]: