Add self-hosted RCS backend, extension, and ops tooling

Ship the Go/SQLite API and Web UI, Chrome/Brave capture addon,
Docker Compose, Pangolin reverse-proxy support, and a user-crontab
watchdog so the binary stays running without systemd.

backend/internal/imgur/imgur.go

@@ -0,0 +1,105 @@
+package imgur
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"mime/multipart"
+	"net/http"
+	"os"
+	"time"
+)
+
+const uploadURL = "https://api.imgur.com/3/image"
+
+// Client uploads images to Imgur anonymously with a Client-ID.
+type Client struct {
+	clientID   string
+	httpClient *http.Client
+}
+
+// New creates an Imgur client. clientID may be empty (uploads will fail clearly).
+func New(clientID string) *Client {
+	return &Client{
+		clientID: clientID,
+		httpClient: &http.Client{
+			Timeout: 60 * time.Second,
+		},
+	}
+}
+
+// Enabled reports whether a Client-ID is configured.
+func (c *Client) Enabled() bool {
+	return c != nil && c.clientID != ""
+}
+
+type uploadResponse struct {
+	Success bool `json:"success"`
+	Data    struct {
+		Link string `json:"link"`
+		ID   string `json:"id"`
+	} `json:"data"`
+	Status int `json:"status"`
+}
+
+// UploadFile uploads a local image file and returns the public Imgur URL.
+func (c *Client) UploadFile(path string) (string, error) {
+	if !c.Enabled() {
+		return "", fmt.Errorf("imgur is not configured (set IMGUR_CLIENT_ID)")
+	}
+
+	file, err := os.Open(path)
+	if err != nil {
+		return "", fmt.Errorf("open screenshot: %w", err)
+	}
+	defer file.Close()
+
+	var body bytes.Buffer
+	writer := multipart.NewWriter(&body)
+	part, err := writer.CreateFormFile("image", "screenshot.png")
+	if err != nil {
+		return "", err
+	}
+	if _, err := io.Copy(part, file); err != nil {
+		return "", err
+	}
+	_ = writer.WriteField("type", "file")
+	if err := writer.Close(); err != nil {
+		return "", err
+	}
+
+	req, err := http.NewRequest(http.MethodPost, uploadURL, &body)
+	if err != nil {
+		return "", err
+	}
+	req.Header.Set("Authorization", "Client-ID "+c.clientID)
+	req.Header.Set("Content-Type", writer.FormDataContentType())
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("imgur request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	raw, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return "", err
+	}
+
+	var parsed uploadResponse
+	if err := json.Unmarshal(raw, &parsed); err != nil {
+		return "", fmt.Errorf("decode imgur response: %w (body=%s)", err, truncate(string(raw), 200))
+	}
+	if !parsed.Success || parsed.Data.Link == "" {
+		return "", fmt.Errorf("imgur upload failed (status=%d): %s", resp.StatusCode, truncate(string(raw), 300))
+	}
+	return parsed.Data.Link, nil
+}
+
+func truncate(s string, n int) string {
+	if len(s) <= n {
+		return s
+	}
+	return s[:n] + "..."
+}