feat: initial Phase 1 implementation — core framework + Docker

- Data types (SManga, SChapter, Page, MangasPage, all Filter variants)
- Source interfaces (Source, CatalogueSource) with MD5-based ID generation matching Tachiyomi/Suwayomi
- HTTP client with per-host rate limiting, cookie jar, and 429 retry
- FlareSolverr v1 client (FLARESOLVERR_URL env)
- Generic GraphQL POST helper
- goquery HTML parser wrappers
- Source registry (panics on duplicate ID)
- Multi-stage Dockerfile (golang:1.26-alpine + distroless) and compose.yml (postgres, flaresolverr, app)

internal/httpclient/headers.go

@@ -0,0 +1,42 @@
+package httpclient
+
+const (
+	androidUA = "Mozilla/5.0 (Linux; Android 10; K) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Mobile Safari/537.36"
+	desktopUA  = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/124.0.0.0 Safari/537.36"
+)
+
+func AndroidUA() string { return androidUA }
+func DesktopUA() string { return desktopUA }
+
+func JSONHeaders() map[string]string {
+	return map[string]string{
+		"Content-Type": "application/json",
+		"Accept":       "application/json",
+	}
+}
+
+func FormHeaders() map[string]string {
+	return map[string]string{
+		"Content-Type": "application/x-www-form-urlencoded",
+	}
+}
+
+func WithRefererHeader(headers map[string]string, referer string) map[string]string {
+	out := clone(headers)
+	out["Referer"] = referer
+	return out
+}
+
+func WithOrigin(headers map[string]string, origin string) map[string]string {
+	out := clone(headers)
+	out["Origin"] = origin
+	return out
+}
+
+func clone(m map[string]string) map[string]string {
+	out := make(map[string]string, len(m)+1)
+	for k, v := range m {
+		out[k] = v
+	}
+	return out
+}