Give the sync progress bar colour and animation

The bar in the Sync popup is now an AnimatedProgressBar: taller, with a
darker track and the theme's accent fill (orange, frost blue in Nord, green
with a gold shine for Christmas). It shows Godot's busy animation until the
server reports progress, glides to each new value, has a soft highlight
sweeping along the filled part inside its rounded corners, and fills and
pops before the result shows. With Reduce animations it only jumps to its
values.

The styles are SyncProgressBar, SyncProgressBarFill and SyncProgressBarText
in every theme. Anim.stop stops a keyed animation without starting an empty
one.

The server now sends sync times as "MM:SS"; the spec is updated from
MusicServer develop (also the linux-package route), and the test data and
screenshots use the new format.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/openapi.json

@@ -84,6 +84,7 @@
             "type": "string"
           },
           "time_spent": {
+            "description": "How long the sync has been running, as minutes and seconds, e.g. \"02:15\"",
             "type": "string"
           }
         },
@@ -447,6 +448,7 @@
             "type": "array"
           },
           "total_time": {
+            "description": "How long the sync took, as minutes and seconds, e.g. \"02:15\"",
             "type": "string"
           }
         },
@@ -885,6 +887,74 @@
         ]
       }
     },
+    "/api/v1/download/linux-package": {
+      "get": {
+        "description": "Redirects to the download URL of the latest MusicPlayer release for Linux (package with installer).",
+        "operationId": "download-client-linux-package",
+        "responses": {
+          "302": {
+            "description": "Found",
+            "headers": {
+              "Location": {
+                "schema": {
+                  "description": "Download URL of the asset",
+                  "type": "string"
+                }
+              }
+            }
+          },
+          "401": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/APIError"
+                }
+              }
+            },
+            "description": "Unauthorized"
+          },
+          "404": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/APIError"
+                }
+              }
+            },
+            "description": "Not Found"
+          },
+          "500": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/APIError"
+                }
+              }
+            },
+            "description": "Internal Server Error"
+          },
+          "502": {
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/APIError"
+                }
+              }
+            },
+            "description": "Bad Gateway"
+          }
+        },
+        "security": [
+          {
+            "bearer": []
+          }
+        ],
+        "summary": "Download the latest client for Linux (package with installer)",
+        "tags": [
+          "download"
+        ]
+      }
+    },
     "/api/v1/download/list": {
       "get": {
         "description": "Returns the file names of the latest MusicPlayer release.",