fix(web): fix Theme Custom CSS endpoint requiring the user to be logged in as the server admin (#4633)

* fix custom css requiring the user to be the admin and logged in

* move theme api to custom endpoint

* add e2e test

server/immich-openapi-specs.json

@@ -4126,6 +4126,27 @@
         ]
       }
     },
+    "/server-info/theme": {
+      "get": {
+        "operationId": "getTheme",
+        "parameters": [],
+        "responses": {
+          "200": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ServerThemeDto"
+                }
+              }
+            },
+            "description": ""
+          }
+        },
+        "tags": [
+          "Server Info"
+        ]
+      }
+    },
     "/server-info/version": {
       "get": {
         "operationId": "getServerVersion",
@@ -7812,6 +7833,17 @@
         ],
         "type": "object"
       },
+      "ServerThemeDto": {
+        "properties": {
+          "theme": {
+            "$ref": "#/components/schemas/SystemConfigThemeDto"
+          }
+        },
+        "required": [
+          "theme"
+        ],
+        "type": "object"
+      },
       "ServerVersionResponseDto": {
         "properties": {
           "major": {