Add image preview support: Krea-tag parsing with modal, file-explorer preview, skill output endpoint, increase execute timeout to 180s

- SkillEndpoint: GET /api/skills/{slug}/output/{filename} for skill output files
- WorkspaceEndpoint: GET /api/workspace/raw for raw file serving (images)
- File-Explorer: Image preview for png/jpg/gif/webp/svg/bmp/ico
- Chat UI: Parse [Krea: filename] tags into clickable chips with image modal
- ToolService: Increase execute timeout from 30s to 180s for long-running skills

Endpoints/WorkspaceEndpoint.cs

@@ -43,6 +43,7 @@ public static class WorkspaceEndpoint
         app.MapGet("/api/workspace/agent/tree", HandleAgentTree);
         app.MapGet("/api/workspace/agent/file", HandleAgentFile);
         app.MapPut("/api/workspace/agent/file", HandleAgentFileSave);
+        app.MapGet("/api/workspace/raw", HandleRawFile);
     }
 
     private static async Task HandleTree(HttpContext ctx)
@@ -421,4 +422,56 @@ public static class WorkspaceEndpoint
             lineCount
         });
     }
+
+    private static readonly Dictionary<string, string> MimeTypes = new(StringComparer.OrdinalIgnoreCase)
+    {
+        { ".png", "image/png" }, { ".jpg", "image/jpeg" }, { ".jpeg", "image/jpeg" },
+        { ".gif", "image/gif" }, { ".webp", "image/webp" }, { ".svg", "image/svg+xml" },
+        { ".bmp", "image/bmp" }, { ".ico", "image/x-icon" },
+        { ".pdf", "application/pdf" },
+        { ".mp4", "video/mp4" }, { ".webm", "video/webm" },
+        { ".mp3", "audio/mpeg" }, { ".wav", "audio/wav" }, { ".ogg", "audio/ogg" },
+    };
+
+    private static async Task HandleRawFile(HttpContext ctx)
+    {
+        var sessionId = ctx.Request.Query["sessionId"].FirstOrDefault();
+        var filePath = ctx.Request.Query["path"].FirstOrDefault();
+
+        if (string.IsNullOrEmpty(filePath))
+        {
+            ctx.Response.StatusCode = 400;
+            return;
+        }
+
+        var db = ctx.RequestServices.GetRequiredService<Gott.Services.DatabaseService>();
+        var session = await db.GetSession(sessionId ?? "");
+        if (session == null || string.IsNullOrEmpty(session.Workspace))
+        {
+            ctx.Response.StatusCode = 400;
+            return;
+        }
+
+        var basePath = Path.GetFullPath(session.Workspace);
+        var targetPath = Path.GetFullPath(Path.Combine(basePath, filePath));
+
+        if (!targetPath.StartsWith(basePath))
+        {
+            ctx.Response.StatusCode = 403;
+            return;
+        }
+
+        if (!File.Exists(targetPath))
+        {
+            ctx.Response.StatusCode = 404;
+            return;
+        }
+
+        var ext = Path.GetExtension(targetPath);
+        var contentType = MimeTypes.GetValueOrDefault(ext, "application/octet-stream");
+
+        ctx.Response.ContentType = contentType;
+        ctx.Response.Headers["Cache-Control"] = "private, max-age=3600";
+        await ctx.Response.SendFileAsync(targetPath);
+    }
 }