Add Radarr client (M1)

Shared arr HTTP client with API error handling, plus Radarr lookup,
add movie, search and quality profile / root folder / status endpoints.
Tested against httptest fixtures.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/arr/types.go

@@ -0,0 +1,54 @@
+package arr
+
+import (
+	"context"
+	"net/http"
+)
+
+// SystemStatus is the subset of /system/status we use.
+type SystemStatus struct {
+	AppName string `json:"appName"`
+	Version string `json:"version"`
+}
+
+// QualityProfile is a Radarr/Sonarr quality profile.
+type QualityProfile struct {
+	ID   int    `json:"id"`
+	Name string `json:"name"`
+}
+
+// RootFolder is a configured library root.
+type RootFolder struct {
+	ID         int    `json:"id"`
+	Path       string `json:"path"`
+	FreeSpace  int64  `json:"freeSpace"`
+	Accessible bool   `json:"accessible"`
+}
+
+// Image is a poster/fanart reference.
+type Image struct {
+	CoverType string `json:"coverType"`
+	URL       string `json:"url,omitempty"`
+	RemoteURL string `json:"remoteUrl,omitempty"`
+}
+
+// SystemStatus fetches /system/status.
+func (c *Client) SystemStatus(ctx context.Context) (SystemStatus, error) {
+	var s SystemStatus
+	err := c.Do(ctx, http.MethodGet, "system/status", nil, nil, &s)
+	return s, err
+}
+
+// QualityProfiles lists quality profiles.
+func (c *Client) QualityProfiles(ctx context.Context) ([]QualityProfile, error) {
+	var p []QualityProfile
+	err := c.Do(ctx, http.MethodGet, "qualityprofile", nil, nil, &p)
+	return p, err
+}
+
+// RootFolders lists root folders.
+func (c *Client) RootFolders(ctx context.Context) ([]RootFolder, error) {
+	var f []RootFolder
+	err := c.Do(ctx, http.MethodGet, "rootfolder", nil, nil, &f)
+	return f, err
+}