Migrate all IPC call sites to typed tauri-specta commands.*

Replace the remaining ~155 untyped invoke() calls across stores, services,
components, and routes with the generated commands.* wrappers from
$lib/api/bindings, so every IPC call is compile-time-checked against the
command signatures.

- Register repository_get_subtitle_url and repository_get_video_download_url
  in specta_builder() and the invoke_handler; regenerate bindings.ts.
- Source duplicated wire types (AutoplaySettings, CacheConfig, Session,
  ConnectivityStatus, audio/video settings, etc.) from bindings.
- Fix two bugs surfaced by the typed wrappers:
  - VideoDownloadButton passed an un-awaited Promise as the stream URL.
  - setAutoplaySettings omitted the required userId argument.
- Update unit tests asserting the old invoke(name, args) shape.
- Remove the five param-naming guard tests; the compiler and codegen now
  enforce what they checked.

svelte-check: 0 errors. vitest: green. cargo test --lib: green.

src/routes/downloads/+page.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
   import { onMount } from "svelte";
   import { goto } from "$app/navigation";
-  import { invoke } from "@tauri-apps/api/core";
+  import { commands } from "$lib/api/bindings";
   import { downloads, activeDownloads, completedDownloads, pendingDownloads, failedDownloads } from "$lib/stores/downloads";
   import { auth } from "$lib/stores/auth";
   import DownloadItem from "$lib/components/downloads/DownloadItem.svelte";
@@ -85,7 +85,7 @@
     try {
       const userId = $auth.user?.id;
       if (userId) {
-        await invoke("clear_stale_downloads", { userId });
+        await commands.clearStaleDownloads(userId);
         await downloads.refresh(userId);
       }
     } catch (error) {
@@ -224,7 +224,7 @@
             const userId = $auth.user?.id;
             if (userId) {
               if (confirm('Delete ALL downloads (including completed)? This cannot be undone.')) {
-                await invoke("delete_all_downloads", { userId });
+                await commands.deleteAllDownloads(userId);
                 await downloads.refresh(userId);
               }
             }