feat(server): add OIDC logout URL override option (#27389)

* feat(server): add OIDC logout URL override option
- Added toggle and field consistent with existing mobile redirect URI override.
- Existing auto-discovery remains default.
- Update tests and docs for new feature.

* fix(server): changes from review for OIDC logout URL override
- Rename 'logoutUri' to 'endSessionEndpoint'
- Remove toggle, just use override if provided
- Moved field in settings UI

server/src/dtos/system-config.dto.ts

@@ -190,6 +190,12 @@ const SystemConfigOAuthSchema = z
       .describe('Issuer URL'),
     scope: z.string().describe('Scope'),
     prompt: z.string().describe('OAuth prompt parameter (e.g. select_account, login, consent)'),
+    endSessionEndpoint: z
+      .string()
+      .refine((url) => url.length === 0 || z.url().safeParse(url).success, {
+        error: 'endSessionEndpoint must be an empty string or a valid URL',
+      })
+      .describe('End session endpoint'),
     signingAlgorithm: z.string().describe('Signing algorithm'),
     profileSigningAlgorithm: z.string().describe('Profile signing algorithm'),
     storageLabelClaim: z.string().describe('Storage label claim'),