feat(assistant): add multi-dialog UX, task-aware llm settings, and i18n cleanup

frontend/src/routes/migration/+page.svelte

@@ -202,7 +202,7 @@
           // Task status update will be handled by store/websocket
       } catch (e) {
           console.error("Failed to resume task:", e);
-          passwordPromptErrorMessage = e.message;
+          passwordPromptErrorMessage = e.message || ($t.migration?.resume_failed || "Failed to resume task");
           // Keep prompt open
       }
   }
@@ -216,15 +216,15 @@
    */
   async function startMigration() {
     if (!sourceEnvId || !targetEnvId) {
-      error = "Please select both source and target environments.";
+      error = $t.migration?.select_both_envs || "Please select both source and target environments.";
       return;
     }
     if (sourceEnvId === targetEnvId) {
-      error = "Source and target environments must be different.";
+      error = $t.migration?.different_envs || "Source and target environments must be different.";
       return;
     }
     if (selectedDashboardIds.length === 0) {
-      error = "Please select at least one dashboard to migrate.";
+      error = $t.migration?.select_dashboards || "Please select at least one dashboard to migrate.";
       return;
     }
 
@@ -249,7 +249,7 @@
         selectedTask.set(task);
       } catch (fetchErr) {
         // Fallback: create a temporary task object to switch view immediately
-        console.warn("Could not fetch task details immediately, using placeholder.");
+        console.warn($t.migration?.task_placeholder_warn || "Could not fetch task details immediately, using placeholder.");
         selectedTask.set({
             id: result.task_id,
             plugin_id: 'superset-migration',
@@ -283,7 +283,7 @@
     </div>
   {:else}
     {#if loading}
-      <p>Loading environments...</p>
+      <p>{$t.migration?.loading_envs || "Loading environments..."}</p>
     {:else if error}
       <div class="bg-red-100 border border-red-400 text-red-700 px-4 py-3 rounded mb-4">
         {error}
@@ -292,12 +292,12 @@
 
     <div class="grid grid-cols-1 md:grid-cols-2 gap-6 mb-8">
       <EnvSelector
-        label="Source Environment"
+        label={$t.migration?.source_env || "Source Environment"}
         bind:selectedId={sourceEnvId}
         {environments}
       />
       <EnvSelector
-        label="Target Environment"
+        label={$t.migration?.target_env || "Target Environment"}
         bind:selectedId={targetEnvId}
         {environments}
       />
@@ -305,7 +305,7 @@
 
     <!-- [DEF:DashboardSelectionSection:Component] -->
     <div class="mb-8">
-      <h2 class="text-lg font-medium mb-4">Select Dashboards</h2>
+      <h2 class="text-lg font-medium mb-4">{$t.migration?.select_dashboards_title || "Select Dashboards"}</h2>
       
       {#if sourceEnvId}
         <DashboardGrid
@@ -314,7 +314,7 @@
           environmentId={sourceEnvId}
         />
       {:else}
-        <p class="text-gray-500 italic">Select a source environment to view dashboards.</p>
+        <p class="text-gray-500 italic">{$t.dashboard?.select_source || "Select a source environment to view dashboards."}</p>
       {/if}
     </div>
     <!-- [/DEF:DashboardSelectionSection:Component] -->
@@ -329,15 +329,15 @@
         class="h-4 w-4 text-indigo-600 focus:ring-indigo-500 border-gray-300 rounded"
       />
       <label for="replace-db" class="ml-2 block text-sm text-gray-900">
-        Replace Database (Apply Mappings)
+        {$t.migration?.replace_db || "Replace Database (Apply Mappings)"}
       </label>
     </div>
 
     {#if replaceDb}
       <div class="mb-8 p-4 border rounded-md bg-gray-50">
-        <h3 class="text-md font-medium mb-4">Database Mappings</h3>
+        <h3 class="text-md font-medium mb-4">{$t.migration?.database_mappings || "Database Mappings"}</h3>
         {#if fetchingDbs}
-          <p>Loading databases and suggestions...</p>
+          <p>{$t.migration?.loading_dbs || "Loading databases and suggestions..."}</p>
         {:else if sourceDatabases.length > 0}
           <MappingTable
             {sourceDatabases}
@@ -351,7 +351,7 @@
             on:click={fetchDatabases}
             class="text-indigo-600 hover:text-indigo-500 text-sm font-medium"
           >
-            Refresh Databases & Suggestions
+            {$t.migration?.refresh_dbs || "Refresh Databases & Suggestions"}
           </button>
         {/if}
       </div>
@@ -361,7 +361,7 @@
       on:click={startMigration}
       disabled={!sourceEnvId || !targetEnvId || sourceEnvId === targetEnvId || selectedDashboardIds.length === 0}
     >
-      Start Migration
+      {$t.migration?.start || "Start Migration"}
     </Button>
   {/if}
 </div>