feat: add drag and drop file support (#64)

src/lib/components/InputBar.svelte

@@ -37,6 +37,7 @@
   let matchingCommands = $state<SlashCommand[]>([]);
   let selectedCommandIndex = $state(0);
   let attachments = $state<Attachment[]>([]);
+  let isDragging = $state(false);
 
   // Input history state
   let inputHistory = $state<string[]>([]);
@@ -301,6 +302,79 @@ User: ${formattedMessage}`;
     claudeStore.removeAttachment(id);
   }
 
+  function getFileTypeFromExtension(extension: string): "image" | "document" | "other" {
+    const imageExtensions = ["png", "jpg", "jpeg", "gif", "webp", "svg", "bmp"];
+    const documentExtensions = ["pdf", "txt", "md", "doc", "docx", "csv", "json", "xml"];
+
+    if (imageExtensions.includes(extension)) {
+      return "image";
+    } else if (documentExtensions.includes(extension)) {
+      return "document";
+    }
+    return "other";
+  }
+
+  function handleDragEnter(event: DragEvent) {
+    event.preventDefault();
+    event.stopPropagation();
+    if (event.dataTransfer?.types.includes("Files")) {
+      isDragging = true;
+    }
+  }
+
+  function handleDragOver(event: DragEvent) {
+    event.preventDefault();
+    event.stopPropagation();
+    if (event.dataTransfer) {
+      event.dataTransfer.dropEffect = "copy";
+    }
+  }
+
+  function handleDragLeave(event: DragEvent) {
+    event.preventDefault();
+    event.stopPropagation();
+    // Only set isDragging to false if we're leaving the form element entirely
+    const relatedTarget = event.relatedTarget as Node | null;
+    const currentTarget = event.currentTarget as HTMLElement;
+    if (!relatedTarget || !currentTarget.contains(relatedTarget)) {
+      isDragging = false;
+    }
+  }
+
+  function handleDrop(event: DragEvent) {
+    event.preventDefault();
+    event.stopPropagation();
+    isDragging = false;
+
+    const files = event.dataTransfer?.files;
+    if (!files || files.length === 0) return;
+
+    for (const file of files) {
+      const filename = file.name;
+      const extension = filename.split(".").pop()?.toLowerCase() || "";
+      const fileType = getFileTypeFromExtension(extension);
+
+      // Create attachment from dropped file
+      // Note: For dropped files, we create a preview URL for images
+      let previewUrl: string | undefined;
+      if (fileType === "image") {
+        previewUrl = URL.createObjectURL(file);
+      }
+
+      const attachment: Attachment = {
+        id: `attachment-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`,
+        filename,
+        path: (file as File & { path?: string }).path || file.name,
+        size: file.size,
+        type: fileType,
+        mimeType: file.type,
+        previewUrl,
+      };
+
+      claudeStore.addAttachment(attachment);
+    }
+  }
+
   async function handleFilePicker() {
     try {
       const selected = await open({
@@ -348,29 +422,15 @@ User: ${formattedMessage}`;
       const files = Array.isArray(selected) ? selected : [selected];
 
       for (const filePath of files) {
-        // Get file info
         const filename = filePath.split(/[/\\]/).pop() || "unknown";
         const extension = filename.split(".").pop()?.toLowerCase() || "";
+        const fileType = getFileTypeFromExtension(extension);
 
-        // Determine file type
-        const imageExtensions = ["png", "jpg", "jpeg", "gif", "webp", "svg", "bmp"];
-        const documentExtensions = ["pdf", "txt", "md", "doc", "docx", "csv", "json", "xml"];
-
-        let fileType: "image" | "document" | "other";
-        if (imageExtensions.includes(extension)) {
-          fileType = "image";
-        } else if (documentExtensions.includes(extension)) {
-          fileType = "document";
-        } else {
-          fileType = "other";
-        }
-
-        // Create attachment
         const attachment: Attachment = {
           id: `attachment-${Date.now()}-${Math.random().toString(36).substr(2, 9)}`,
           filename,
           path: filePath,
-          size: 0, // We don't have easy access to file size from the dialog
+          size: 0,
           type: fileType,
         };
 
@@ -444,7 +504,15 @@ User: ${formattedMessage}`;
   }
 </script>
 
-<form onsubmit={handleSubmit} class="input-bar">
+<form
+  onsubmit={handleSubmit}
+  ondragenter={handleDragEnter}
+  ondragover={handleDragOver}
+  ondragleave={handleDragLeave}
+  ondrop={handleDrop}
+  class="input-bar"
+  class:is-dragging={isDragging}
+>
   <AttachmentPreview {attachments} onRemove={handleRemoveAttachment} />
 
   <div class="input-controls flex gap-2 mb-2">
@@ -532,6 +600,33 @@ User: ${formattedMessage}`;
     display: flex;
     flex-direction: column;
     gap: 8px;
+    position: relative;
+    transition: border-color 0.2s, background 0.2s;
+  }
+
+  .input-bar.is-dragging {
+    background: var(--bg-secondary);
+    border: 2px dashed var(--accent-primary);
+    border-radius: 12px;
+    padding: 8px;
+  }
+
+  .input-bar.is-dragging::before {
+    content: "Drop files here";
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    font-size: 18px;
+    font-weight: 500;
+    color: var(--accent-primary);
+    pointer-events: none;
+    z-index: 10;
+  }
+
+  .input-bar.is-dragging > * {
+    opacity: 0.3;
+    pointer-events: none;
   }
 
   .input-controls {