Add ability to choose export format in UI

Author: caleb531

desktop-app/src/routes/transcript/+page.svelte

@@ -1,13 +1,14 @@
 <script lang="ts">
     import { invoke } from '@tauri-apps/api/core';
     import { revealItemInDir } from '@tauri-apps/plugin-opener';
-    import { Button } from 'carbon-components-svelte';
+    import { Button, Select, SelectItem } from 'carbon-components-svelte';
     import InlineNotification from '../../components/InlineNotification.svelte';
     import { invokeIcaCsvToFile, MissingContactError } from '../../lib/cli';
 
-    const baseFilename = 'transcript.csv';
+    const baseFilename = 'transcript';
 
     let isExporting = $state(false);
+    let format = $state<'csv' | 'xlsx'>('csv');
     let errorMessage = $state('');
     let successMessage = $state('');
     let exportedFilePath = $state('');
@@ -19,8 +20,9 @@
         successMessage = '';
 
         try {
+            const filename = `${baseFilename}.${format}`;
             const outputPath = await invoke<string>('resolve_download_output_path', {
-                baseName: baseFilename
+                baseName: filename
             });
             await invokeIcaCsvToFile(['transcript'], outputPath);
             exportedFilePath = outputPath;
@@ -54,14 +56,25 @@
         <header>
             <h2>Transcript</h2>
             <p class="transcript-export__description">
-                Export your full conversation transcript to CSV in Downloads. The filename will be
-                incremented when needed (for example, transcript-1.csv).
+                Export your full conversation transcript in your selected format to Downloads. The
+                filename will be incremented when needed (for example, transcript-1.csv).
             </p>
         </header>
 
         <form class="transcript-export__form" onsubmit={exportTranscript}>
+            <div class="transcript-export__format">
+                <Select labelText="Format" bind:selected={format} disabled={isExporting}>
+                    <SelectItem value="csv" text="CSV" />
+                    <SelectItem value="xlsx" text="Excel" />
+                </Select>
+            </div>
+
             <Button type="submit" kind="primary" disabled={isExporting}>
-                {isExporting ? 'Exporting…' : 'Export Transcript CSV'}
+                {#if isExporting}
+                    Exporting…
+                {:else}
+                    Export Transcript
+                {/if}
             </Button>
         </form>
 
@@ -106,6 +119,15 @@
 
     .transcript-export__form {
         margin-top: 1.5rem;
+        display: flex;
+        flex-direction: row;
+        align-items: flex-end;
+        justify-content: center;
+        gap: 1rem;
+    }
+
+    .transcript-export__format {
+        width: 12rem;
     }
 
     .transcript-export__notification {