feat: implement file upload handler and related functionality

- Added file upload handler to process both multipart and raw file uploads.
- Implemented parsing logic for upload requests, including handling file metadata.
- Introduced SaveFileDecodedInput structure for handling decoded file uploads.
- Created unit tests for file upload parsing and validation.

feat: add metadata retry configuration and functionality

- Introduced MetadataRetryConfig to the application configuration.
- Implemented MetadataRetryer to handle retrying metadata extraction for thoughts.
- Added new tool for retrying failed metadata extractions.
- Updated thought metadata structure to include status and timestamps for metadata processing.

fix: enhance metadata normalization and error handling

- Updated metadata normalization functions to track status and errors.
- Improved handling of metadata extraction failures during thought updates and captures.
- Ensured that metadata status is correctly set during various operations.

refactor: streamline file saving logic in FilesTool

- Refactored Save method in FilesTool to utilize new SaveDecoded method.
- Simplified project and thought ID resolution logic during file saving.

internal/app/files_test.go

@@ -0,0 +1,57 @@
+package app
+
+import (
+	"bytes"
+	"mime/multipart"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestParseRawUploadRequiresName(t *testing.T) {
+	req := httptest.NewRequest(http.MethodPost, "/files", bytes.NewReader([]byte("hello")))
+	req.Header.Set("Content-Type", "application/octet-stream")
+
+	_, err := parseRawUpload(req)
+	if err == nil {
+		t.Fatal("expected error for missing name")
+	}
+}
+
+func TestParseMultipartUploadUsesFileMetadata(t *testing.T) {
+	var body bytes.Buffer
+	writer := multipart.NewWriter(&body)
+
+	part, err := writer.CreateFormFile("file", "note.txt")
+	if err != nil {
+		t.Fatalf("create form file: %v", err)
+	}
+	if _, err := part.Write([]byte("hello world")); err != nil {
+		t.Fatalf("write form file: %v", err)
+	}
+	_ = writer.WriteField("project", "amcs")
+	_ = writer.WriteField("kind", "document")
+	if err := writer.Close(); err != nil {
+		t.Fatalf("close writer: %v", err)
+	}
+
+	req := httptest.NewRequest(http.MethodPost, "/files", &body)
+	req.Header.Set("Content-Type", writer.FormDataContentType())
+
+	got, err := parseMultipartUpload(req)
+	if err != nil {
+		t.Fatalf("parse multipart upload: %v", err)
+	}
+	if got.Name != "note.txt" {
+		t.Fatalf("name = %q, want note.txt", got.Name)
+	}
+	if string(got.Content) != "hello world" {
+		t.Fatalf("content = %q, want hello world", string(got.Content))
+	}
+	if got.Project != "amcs" {
+		t.Fatalf("project = %q, want amcs", got.Project)
+	}
+	if got.Kind != "document" {
+		t.Fatalf("kind = %q, want document", got.Kind)
+	}
+}