v2 restructure: Go client, Docker engine, release tooling

- Remove v1 Python CLI (src/kb_search/, tests/, root pyproject.toml, uv.lock, .venv)
- Add Go client with cross-platform build (client/)
- Add FastAPI engine with NVIDIA and multi-stage ROCm Dockerfiles (engine/)
- Add VERSION files for client and engine, wired into builds
- Add release.sh for automated build, tag, release, and Docker push
- Update README with build/release docs and ROCm migration note
- Clean up .gitignore for v2 project structure

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client/internal/api/client.go

@@ -0,0 +1,158 @@
+package api
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"mime/multipart"
+	"net/http"
+
+	"github.com/kb-search/kb/internal/config"
+)
+
+// FileUpload describes a file to include in a multipart request.
+type FileUpload struct {
+	FieldName string
+	FileName  string
+	Reader    io.Reader
+}
+
+// Client is an HTTP client for the kb-search engine API.
+type Client struct {
+	baseURL    string
+	apiKey     string
+	httpClient *http.Client
+}
+
+// NewClient creates a Client from the current configuration.
+func NewClient() *Client {
+	cfg := config.Get()
+	return &Client{
+		baseURL:    cfg.EngineURL,
+		apiKey:     cfg.APIKey,
+		httpClient: &http.Client{},
+	}
+}
+
+func (c *Client) newRequest(method, path string, body io.Reader) (*http.Request, error) {
+	url := c.baseURL + path
+	req, err := http.NewRequest(method, url, body)
+	if err != nil {
+		return nil, err
+	}
+	if c.apiKey != "" {
+		req.Header.Set("Authorization", "Bearer "+c.apiKey)
+	}
+	return req, nil
+}
+
+func (c *Client) do(req *http.Request) (*http.Response, error) {
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("Cannot reach engine at %s: %v", c.baseURL, err)
+	}
+	return resp, nil
+}
+
+// Get performs a GET request to the given path.
+func (c *Client) Get(path string) (*http.Response, error) {
+	req, err := c.newRequest(http.MethodGet, path, nil)
+	if err != nil {
+		return nil, err
+	}
+	return c.do(req)
+}
+
+// Post performs a POST request with a JSON body.
+func (c *Client) Post(path string, body interface{}) (*http.Response, error) {
+	data, err := json.Marshal(body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal request body: %w", err)
+	}
+	req, err := c.newRequest(http.MethodPost, path, bytes.NewReader(data))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	return c.do(req)
+}
+
+// PostMultipart performs a POST request with multipart/form-data encoding.
+func (c *Client) PostMultipart(path string, fields map[string]string, file *FileUpload) (*http.Response, error) {
+	var buf bytes.Buffer
+	w := multipart.NewWriter(&buf)
+
+	for k, v := range fields {
+		if err := w.WriteField(k, v); err != nil {
+			return nil, fmt.Errorf("failed to write field %s: %w", k, err)
+		}
+	}
+
+	if file != nil {
+		part, err := w.CreateFormFile(file.FieldName, file.FileName)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create form file: %w", err)
+		}
+		if _, err := io.Copy(part, file.Reader); err != nil {
+			return nil, fmt.Errorf("failed to copy file data: %w", err)
+		}
+	}
+
+	if err := w.Close(); err != nil {
+		return nil, fmt.Errorf("failed to close multipart writer: %w", err)
+	}
+
+	req, err := c.newRequest(http.MethodPost, path, &buf)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", w.FormDataContentType())
+	return c.do(req)
+}
+
+// Delete performs a DELETE request to the given path.
+func (c *Client) Delete(path string) (*http.Response, error) {
+	req, err := c.newRequest(http.MethodDelete, path, nil)
+	if err != nil {
+		return nil, err
+	}
+	return c.do(req)
+}
+
+// Put performs a PUT request with a JSON body.
+func (c *Client) Put(path string, body interface{}) (*http.Response, error) {
+	data, err := json.Marshal(body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to marshal request body: %w", err)
+	}
+	req, err := c.newRequest(http.MethodPut, path, bytes.NewReader(data))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	return c.do(req)
+}
+
+// DecodeJSON reads the response body and decodes it into target.
+func DecodeJSON(resp *http.Response, target interface{}) error {
+	defer resp.Body.Close()
+	return json.NewDecoder(resp.Body).Decode(target)
+}
+
+// CheckError returns a formatted error for non-2xx responses, or nil on success.
+func CheckError(resp *http.Response) error {
+	if resp.StatusCode >= 200 && resp.StatusCode < 300 {
+		return nil
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+
+	var errResp struct {
+		Detail string `json:"detail"`
+	}
+	if json.Unmarshal(body, &errResp) == nil && errResp.Detail != "" {
+		return fmt.Errorf("API error (%d): %s", resp.StatusCode, errResp.Detail)
+	}
+	return fmt.Errorf("API error (%d): %s", resp.StatusCode, string(body))
+}