Cleanup: infer a missing sex from a known-sex spouse (preview → approve)

Unset sex renders blue (male-colored), which is misleading next to a confirmed
male partner. Add a Cleanup action that proposes the opposite sex for an unset
partner of someone whose sex is set (couples are opposite-sex in practice — a
confirmed-male husband ⇒ a female wife). People whose known partners disagree
are skipped as ambiguous.

It's a preview the user reviews and approves in the Cleanup tool (reusing the
existing gender apply path + audit) — not an autonomous write. Backend:
guess_gender_by_spouse + GET /cleanup/gender/from-spouse. Frontend: an "Infer
from spouse" button feeding the existing proposal list. Test covers
propose-opposite, skip-no-partner, skip-already-set, apply, and re-preview.

Full suite 73 passed; frontend build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/app/trees/[id]/cleanup/page.tsx

@@ -109,6 +109,15 @@ export default function CleanupPage() {
     setGenSel(new Set((data ?? []).map((g) => g.person_id)));
   }
 
+  async function guessGenderFromSpouse() {
+    setGenMsg(null);
+    const { data } = await api.GET("/api/v1/trees/{tree_id}/cleanup/gender/from-spouse", {
+      params: { path: { tree_id: treeId } },
+    });
+    setGender(data ?? []);
+    setGenSel(new Set((data ?? []).map((g) => g.person_id)));
+  }
+
   async function applyGender() {
     const updates = (gender ?? [])
       .filter((g) => genSel.has(g.person_id))
@@ -246,10 +255,15 @@ export default function CleanupPage() {
             <Button variant="outline" onClick={guessGender}>
               Guess from first name
             </Button>
+            <Button variant="outline" onClick={guessGenderFromSpouse}>
+              Infer from spouse
+            </Button>
           </div>
           <p className="text-xs text-[var(--muted)]">
-            “Guess from first name” uses a built-in name dictionary for people with no sex set;
-            ambiguous names (Marion, Frances, …) are left for you to decide.
+            “Guess from first name” uses a built-in name dictionary for people with no sex set.
+            “Infer from spouse” sets the opposite sex for an unset partner of someone whose sex is
+            known (e.g. a confirmed-male husband ⇒ a female wife) — review before applying, since
+            it assumes opposite-sex couples.
           </p>
           {genMsg && <p className="text-sm text-bronze">{genMsg}</p>}
           {gender && (