Account menu + Settings (change password); per-tree home person; full-width tree

- Sidebar bottom-left now shows the signed-in user; clicking opens a menu with
  Settings and Sign out. New /settings page: account info + change password
  (POST /auth/change-password, re-verifies current password). Export/restore/
  delete are stubbed there for the next pass.
- Per-tree default/home person: tree.home_person_id (migration) + TreeUpdate/
  Read; the tree and family views open focused on it; the person page gets a
  "Set as default" control and "Default person" badge. Cleared if that person
  is deleted. Complements the account-level "this is me" link.
- Tree visualization now fills the content area (AppShell drops the max-width
  column on the /tree route); other pages stay centered.
- Audit records are coerced JSON-safe (UUIDs/enums), so PATCHing UUID fields
  like home_person_id audits cleanly.

50 backend tests pass; migration up/down verified; frontend builds.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/openapi.json

@@ -259,6 +259,40 @@
         }
       }
     },
+    "/api/v1/auth/change-password": {
+      "post": {
+        "tags": [
+          "auth"
+        ],
+        "summary": "Change Password",
+        "operationId": "change_password_api_v1_auth_change_password_post",
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/PasswordChange"
+              }
+            }
+          },
+          "required": true
+        },
+        "responses": {
+          "204": {
+            "description": "Successful Response"
+          },
+          "422": {
+            "description": "Validation Error",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/HTTPValidationError"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/users/me": {
       "get": {
         "tags": [
@@ -3890,6 +3924,25 @@
         "title": "ParentChildQualifier",
         "description": "Qualifies a parent_child edge so adoption/donor/blended families are\nfirst-class rather than edge cases (ARCHITECTURE \u00a75)."
       },
+      "PasswordChange": {
+        "properties": {
+          "current_password": {
+            "type": "string",
+            "title": "Current Password"
+          },
+          "new_password": {
+            "type": "string",
+            "minLength": 8,
+            "title": "New Password"
+          }
+        },
+        "type": "object",
+        "required": [
+          "current_password",
+          "new_password"
+        ],
+        "title": "PasswordChange"
+      },
       "PasswordResetConfirm": {
         "properties": {
           "token": {
@@ -4702,6 +4755,18 @@
             "format": "uuid",
             "title": "Owner Id"
           },
+          "home_person_id": {
+            "anyOf": [
+              {
+                "type": "string",
+                "format": "uuid"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Home Person Id"
+          },
           "created_at": {
             "type": "string",
             "format": "date-time",
@@ -4752,6 +4817,18 @@
                 "type": "null"
               }
             ]
+          },
+          "home_person_id": {
+            "anyOf": [
+              {
+                "type": "string",
+                "format": "uuid"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Home Person Id"
           }
         },
         "type": "object",