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/config/config.go

@@ -0,0 +1,55 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// Config holds runtime settings for the RCS backend.
+type Config struct {
+	Addr          string
+	DataDir       string
+	DBPath        string
+	ScreenshotDir string
+	APIKey        string
+	ImgurClientID string
+	// PublicBaseURL is the canonical public origin (e.g. https://rcs.example.com).
+	PublicBaseURL string
+	// TrustProxy honors X-Forwarded-Proto / X-Forwarded-Host when behind a reverse proxy.
+	TrustProxy bool
+}
+
+// Load reads configuration from environment variables with sensible defaults.
+func Load() Config {
+	dataDir := envOr("RCS_DATA_DIR", "data")
+	dbPath := envOr("RCS_DB_PATH", filepath.Join(dataDir, "rcs.db"))
+	screenshotDir := filepath.Join(dataDir, "screenshots")
+
+	return Config{
+		Addr:          envOr("RCS_ADDR", "127.0.0.1:8080"),
+		DataDir:       dataDir,
+		DBPath:        dbPath,
+		ScreenshotDir: screenshotDir,
+		APIKey:        os.Getenv("RCS_API_KEY"),
+		ImgurClientID: os.Getenv("IMGUR_CLIENT_ID"),
+		PublicBaseURL: strings.TrimRight(os.Getenv("RCS_PUBLIC_BASE_URL"), "/"),
+		TrustProxy:    envTruthy("RCS_TRUST_PROXY"),
+	}
+}
+
+func envOr(key, fallback string) string {
+	if value := os.Getenv(key); value != "" {
+		return value
+	}
+	return fallback
+}
+
+func envTruthy(key string) bool {
+	switch strings.ToLower(strings.TrimSpace(os.Getenv(key))) {
+	case "1", "true", "yes", "on":
+		return true
+	default:
+		return false
+	}
+}