refactor(auth): remove redirect_uri parameter from OAuth flow

Simplify OAuth login and account linking by removing the redirect_uri
parameter from initiateLogin and initiateLink functions. The backend
now handles callback URL construction internally.

src/lib/api.ts

@@ -902,9 +902,8 @@ export const api = {
       request<LinkedAccountsResponse>('/auth/external/linked-accounts'),
 
     // Initiate OAuth login flow — returns authorization_url to redirect the browser to
-    initiateLogin: (provider: string, options?: { redirect_uri?: string; organization_id?: string; flow?: string; oidc_session_id?: string }) => {
+    initiateLogin: (provider: string, options?: { organization_id?: string; flow?: string; oidc_session_id?: string }) => {
       const params = new URLSearchParams({ flow: options?.flow ?? 'login' });
-      if (options?.redirect_uri) params.set('redirect_uri', options.redirect_uri);
       if (options?.organization_id) params.set('organization_id', options.organization_id);
       if (options?.oidc_session_id) params.set('oidc_session_id', options.oidc_session_id);
       return request<OAuthAuthorizeResponse>(`/auth/external/${provider}/authorize?${params.toString()}`, {
@@ -914,10 +913,9 @@ export const api = {
     },
 
     // Initiate account linking flow (requires auth)
-    initiateLink: (provider: string, redirect_uri?: string) =>
+    initiateLink: (provider: string) =>
       request<OAuthAuthorizeResponse>(`/auth/external/${provider}/link`, {
         method: 'POST',
-        body: JSON.stringify({ redirect_uri }),
         credentials: 'include',
       }),