feat(join): implement A4 join household page (/join/[token])

- schema.d.ts: add GET /v1/invites/{code}, InviteInfoResponse, AcceptInviteRequest; update acceptInvite operation
- hooks.server.ts: add /join to PUBLIC_ROUTES; redirect authenticated users on /join/* to /
- +page.server.ts: load validates token (invalid:true on 404); action creates account + joins + sets session cookie
- HouseholdIdentityPanel.svelte: logo, household name (Fraunces), inviter text, static permissions list
- JoinForm.svelte: name/email/password + show/hide toggle, "Haushalt beitreten" CTA, field errors, pre-fill
- +page.svelte: no-chrome layout, mobile (banner+form stacked) / desktop (400px panel + flex:1) split, invalid-token inline state

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/api/schema.d.ts

@@ -148,6 +148,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/v1/invites/{code}": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get: operations["getInviteInfo"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/v1/invites/{code}/accept": {
         parameters: {
             query?: never;
@@ -739,6 +755,20 @@ export interface components {
             data?: components["schemas"]["AcceptInviteResponse"];
             meta?: components["schemas"]["Meta"];
         };
+        InviteInfoResponse: {
+            householdName?: string;
+            inviterName?: string;
+        };
+        ApiResponseInviteInfoResponse: {
+            status?: string;
+            data?: components["schemas"]["InviteInfoResponse"];
+            meta?: components["schemas"]["Meta"];
+        };
+        AcceptInviteRequest: {
+            name: string;
+            email: string;
+            password: string;
+        };
         Meta: {
             pagination?: components["schemas"]["Pagination"];
         };
@@ -1345,7 +1375,7 @@ export interface operations {
             };
         };
     };
-    acceptInvite: {
+    getInviteInfo: {
         parameters: {
             query?: never;
             header?: never;
@@ -1355,6 +1385,37 @@ export interface operations {
             cookie?: never;
         };
         requestBody?: never;
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "*/*": components["schemas"]["ApiResponseInviteInfoResponse"];
+                };
+            };
+            /** @description Not found */
+            404: {
+                headers: { [name: string]: unknown };
+                content: { "*/*": components["schemas"]["ApiError"] };
+            };
+        };
+    };
+    acceptInvite: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                code: string;
+            };
+            cookie?: never;
+        };
+        requestBody: {
+            content: {
+                "application/json": components["schemas"]["AcceptInviteRequest"];
+            };
+        };
         responses: {
             /** @description OK */
             200: {
@@ -1365,6 +1426,16 @@ export interface operations {
                     "*/*": components["schemas"]["ApiResponseAcceptInviteResponse"];
                 };
             };
+            /** @description Email already registered */
+            409: {
+                headers: { [name: string]: unknown };
+                content: { "*/*": components["schemas"]["ApiError"] };
+            };
+            /** @description Invite not found or invalid */
+            404: {
+                headers: { [name: string]: unknown };
+                content: { "*/*": components["schemas"]["ApiError"] };
+            };
         };
     };
     listCategories: {