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/openapi.json

@@ -2915,6 +2915,54 @@
         }
       }
     },
+    "/api/v1/trees/{tree_id}/cleanup/gender/from-spouse": {
+      "get": {
+        "tags": [
+          "cleanup"
+        ],
+        "summary": "Guess Gender From Spouse",
+        "description": "Infer a missing sex from a partner whose sex is set (opposite-sex couple).",
+        "operationId": "guess_gender_from_spouse_api_v1_trees__tree_id__cleanup_gender_from_spouse_get",
+        "parameters": [
+          {
+            "name": "tree_id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string",
+              "format": "uuid",
+              "title": "Tree Id"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Successful Response",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "array",
+                  "items": {
+                    "$ref": "#/components/schemas/GenderProposal"
+                  },
+                  "title": "Response Guess Gender From Spouse Api V1 Trees  Tree Id  Cleanup Gender From Spouse Get"
+                }
+              }
+            }
+          },
+          "422": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/trees/{tree_id}/cleanup/gender": {
       "post": {
         "tags": [