fix(tauri-app): use absolute AppView URL for /api/profile fetch

The Tauri webview's origin is the Vite dev server (port 1430), not
the AppView (port 2584). A relative `fetch('/api/profile/…')`
resolves against Vite, which has no proxy configured, so the
request lands on Vite's 404 HTML page and `response.json()` then
throws `SyntaxError: The string did not match the expected
pattern.` The error surfaced as `err: SyntaxError…` under the
banner of the redesigned ProfileView.

Fix: expose the AppView base URL the Tauri shell was started with
as a sync `get_api_urls` Tauri command. The Rust side reads the
URL from `MAARCADETWEET_APPVIEW_URL` (default
`http://127.0.0.1:2584`) at startup and stores it on `AppState`
so the command doesn't need to re-read the env. The frontend
exposes a cached `getAppviewUrl()` helper; ProfileView's
`load()` uses it to build an absolute fetch URL.

The relative-path bug also affected the previous UserProfileView,
but it never errored loudly enough for the user to notice — the
new X-style layout made the err block visible.

crates/tauri-app/src-tauri/src/lib.rs

@@ -543,8 +543,9 @@ pub fn run() {
         .unwrap_or_else(|_| "http://127.0.0.1:2584".to_string());
 
     let state = AppState {
-        pds: PdsHttpClient::new(pds_url),
-        appview: AppViewClient::new(appview_url),
+        pds: PdsHttpClient::new(pds_url.clone()),
+        appview: AppViewClient::new(appview_url.clone()),
+        appview_url,
         store: store::SessionStore::new(),
     };
 
@@ -722,6 +723,7 @@ pub fn run() {
             open_external_url,
             profile_get_record,
             profile_set,
+            get_api_urls,
         ])
         .run(tauri::generate_context!())
         .expect("error while running maarcadetweet");
@@ -741,6 +743,32 @@ async fn profile_get_record(
         .map_err(|e| e.to_string())
 }
 
+/// Frontend-side base URLs the Tauri shell was started with. Used by
+/// the Svelte components to build absolute fetch URLs — a relative
+/// `/api/...` resolves against the Vite dev origin (port 1430), not
+/// the AppView (port 2584), and the Vite server has no proxy
+/// configured, so the fetch lands on a 404 HTML page and
+/// `response.json()` throws `SyntaxError`.
+#[derive(serde::Serialize)]
+#[serde(rename_all = "camelCase")]
+struct ApiUrls {
+    pds_url: String,
+    appview_url: String,
+}
+
+#[tauri::command]
+fn get_api_urls(state: tauri::State<'_, AppState>) -> ApiUrls {
+    // Sync command — the URLs are immutable for the lifetime of the
+    // Tauri shell (read from MAARCADETWEET_*_URL at startup), so no
+    // async machinery is needed. Returns the AppView URL the
+    // frontend needs; PDS URL is exposed too so future fetch-based
+    // XRPC calls don't have to add their own command.
+    ApiUrls {
+        pds_url: state.pds.base_url.clone(),
+        appview_url: state.appview_url.clone(),
+    }
+}
+
 #[tauri::command]
 async fn profile_set(
     state: tauri::State<'_, AppState>,

crates/tauri-app/src-tauri/src/state.rs

@@ -1,5 +1,10 @@
 pub struct AppState {
     pub pds: crate::pds_client::PdsHttpClient,
     pub appview: crate::appview_client::AppViewClient,
+    /// Base URL of the AppView service (`http://host:port`, no
+    /// trailing slash). Stored verbatim so the frontend can build
+    /// absolute URLs for fetch calls — a relative `/api/profile/…`
+    /// would resolve against the Vite dev origin, not the AppView.
+    pub appview_url: String,
     pub store: crate::store::SessionStore,
 }