feat: require login for upload command

Upload now requires authentication and sends Bearer token.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

artdag.py

@@ -363,14 +363,28 @@ def import_file(filepath):
 @cli.command()
 @click.argument("filepath", type=click.Path(exists=True))
 def upload(filepath):
-    """Upload a file to cache (works with remote servers)."""
+    """Upload a file to cache (works with remote servers). Requires login."""
+    # Check auth
+    token_data = load_token()
+    if not token_data.get("access_token"):
+        click.echo("Not logged in. Please run: artdag login <username>", err=True)
+        sys.exit(1)
+
+    try:
         with open(filepath, "rb") as f:
             files = {"file": (Path(filepath).name, f)}
-        resp = requests.post(f"{get_server()}/cache/upload", files=files)
+            headers = {"Authorization": f"Bearer {token_data['access_token']}"}
+            resp = requests.post(f"{get_server()}/cache/upload", files=files, headers=headers)
+            if resp.status_code == 401:
+                click.echo("Authentication failed. Please login again.", err=True)
+                sys.exit(1)
             resp.raise_for_status()
             result = resp.json()
         click.echo(f"Uploaded: {result['content_hash']}")
         click.echo(f"Size: {result['size']} bytes")
+    except requests.RequestException as e:
+        click.echo(f"Upload failed: {e}", err=True)
+        sys.exit(1)
 
 
 @cli.command()