feat: add native clipboard support for screenshot paste (#67)

## Summary
- Adds Tauri clipboard-manager plugin to read images from native clipboard
- Falls back to native clipboard when WebView clipboard API returns empty (fixes screenshot paste)
- Allows sending messages with just attachments (no text required)
- Logs attached files to output with 📎 emoji

## Test plan
- [ ] Build and run the app natively on Windows
- [ ] Copy a screenshot (Win+Shift+S) and paste in the chat input
- [ ] Verify the screenshot appears as an attachment preview
- [ ] Send the attachment and verify Claude receives the file path
- [ ] Test sending a message with only an attachment (no text)
- [ ] Verify the 📎 log line shows the attached filename

**Note:** Paste will not work in WSLg dev environment due to clipboard isolation - needs native Windows build to test.

✨ This PR was created with help from Hikari~ 🌸

Co-authored-by: Hikari <hikari@nhcarrigan.com>
Reviewed-on: #67
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

src/lib/components/AttachmentPreview.svelte

@@ -0,0 +1,209 @@
+<script lang="ts">
+  import type { Attachment } from "$lib/types/messages";
+
+  interface Props {
+    attachments: Attachment[];
+    onRemove: (id: string) => void;
+  }
+
+  let { attachments, onRemove }: Props = $props();
+
+  function formatFileSize(bytes: number): string {
+    if (bytes < 1024) return `${bytes} B`;
+    if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
+    return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+  }
+
+  function getFileIcon(type: Attachment["type"]): string {
+    switch (type) {
+      case "image":
+        return "🖼️";
+      case "document":
+        return "📄";
+      default:
+        return "📎";
+    }
+  }
+</script>
+
+{#if attachments.length > 0}
+  <div class="attachment-preview-container">
+    <div class="attachment-header">
+      <span class="attachment-count"
+        >{attachments.length} attachment{attachments.length !== 1 ? "s" : ""}</span
+      >
+    </div>
+    <div class="attachment-list">
+      {#each attachments as attachment (attachment.id)}
+        <div class="attachment-item" class:is-image={attachment.type === "image"}>
+          {#if attachment.type === "image" && attachment.previewUrl}
+            <div class="image-preview">
+              <img src={attachment.previewUrl} alt={attachment.filename} />
+            </div>
+          {:else}
+            <div class="file-icon">
+              {getFileIcon(attachment.type)}
+            </div>
+          {/if}
+          <div class="attachment-info">
+            <span class="attachment-filename" title={attachment.filename}>
+              {attachment.filename}
+            </span>
+            <span class="attachment-size">
+              {formatFileSize(attachment.size)}
+            </span>
+          </div>
+          <button
+            type="button"
+            class="remove-button"
+            onclick={() => onRemove(attachment.id)}
+            title="Remove attachment"
+          >
+            <svg
+              width="14"
+              height="14"
+              viewBox="0 0 24 24"
+              fill="none"
+              stroke="currentColor"
+              stroke-width="2"
+              stroke-linecap="round"
+              stroke-linejoin="round"
+            >
+              <line x1="18" y1="6" x2="6" y2="18"></line>
+              <line x1="6" y1="6" x2="18" y2="18"></line>
+            </svg>
+          </button>
+        </div>
+      {/each}
+    </div>
+  </div>
+{/if}
+
+<style>
+  .attachment-preview-container {
+    display: flex;
+    flex-direction: column;
+    gap: 8px;
+    padding: 8px;
+    background: var(--bg-secondary);
+    border: 1px solid var(--border-color);
+    border-radius: 8px;
+    margin-bottom: 8px;
+  }
+
+  .attachment-header {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+  }
+
+  .attachment-count {
+    font-size: 12px;
+    color: var(--text-secondary);
+  }
+
+  .attachment-list {
+    display: flex;
+    flex-wrap: wrap;
+    gap: 8px;
+  }
+
+  .attachment-item {
+    display: flex;
+    align-items: center;
+    gap: 8px;
+    padding: 6px 8px;
+    background: var(--bg-tertiary);
+    border: 1px solid var(--border-color);
+    border-radius: 6px;
+    max-width: 200px;
+    position: relative;
+  }
+
+  .attachment-item.is-image {
+    flex-direction: column;
+    padding: 4px;
+    max-width: 120px;
+  }
+
+  .image-preview {
+    width: 100%;
+    max-width: 110px;
+    max-height: 80px;
+    border-radius: 4px;
+    overflow: hidden;
+    background: var(--bg-primary);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+  }
+
+  .image-preview img {
+    max-width: 100%;
+    max-height: 80px;
+    object-fit: contain;
+  }
+
+  .file-icon {
+    font-size: 24px;
+    flex-shrink: 0;
+  }
+
+  .attachment-info {
+    display: flex;
+    flex-direction: column;
+    gap: 2px;
+    overflow: hidden;
+    flex: 1;
+  }
+
+  .is-image .attachment-info {
+    width: 100%;
+    padding: 0 4px;
+  }
+
+  .attachment-filename {
+    font-size: 12px;
+    color: var(--text-primary);
+    white-space: nowrap;
+    overflow: hidden;
+    text-overflow: ellipsis;
+  }
+
+  .attachment-size {
+    font-size: 10px;
+    color: var(--text-secondary);
+  }
+
+  .remove-button {
+    position: absolute;
+    top: -6px;
+    right: -6px;
+    width: 20px;
+    height: 20px;
+    padding: 0;
+    background: var(--bg-primary);
+    border: 1px solid var(--border-color);
+    border-radius: 50%;
+    color: var(--text-secondary);
+    cursor: pointer;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    opacity: 0;
+    transition:
+      opacity 0.2s,
+      background 0.2s,
+      color 0.2s;
+  }
+
+  .attachment-item:hover .remove-button {
+    opacity: 1;
+  }
+
+  .remove-button:hover {
+    background: var(--error-color, #ef4444);
+    border-color: var(--error-color, #ef4444);
+    color: white;
+  }
+</style>