feat(server/m7-recurring-scans): admin schedule HTTP handlers

Two new endpoints under existing RequireAdmin middleware:
- GET /api/admin/scan/schedule — returns config + computed
  next_scheduled_at (ISO 8601; null when mode='off')
- PATCH /api/admin/scan/schedule — validates per-mode required
  fields, normalizes mode='off' to NULL the per-mode fields,
  writes via UpdateScanSchedule, calls scheduler.Refresh(), returns
  the updated record.

server.New + api.Mount gain a *library.Scheduler parameter; handlers
struct + Server struct gain the scheduler field. Test stubs
(server_test.go, library_test.go's Mount call) updated to pass nil.

Tests gated on MINSTREL_TEST_DATABASE_URL: GET default is mode=off
with null next; PATCH daily produces a 03:00 next-fire; PATCH
weekly without weekly_day → 400; PATCH off normalizes lingering
per-mode fields to NULL; non-admin → 403.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/server/server.go

@@ -77,10 +77,11 @@ type Server struct {
 	CoverSettings       *coverart.SettingsService
 	LibraryScanner      *library.Scanner
 	ScanCfg             library.RunScanConfig
+	Scheduler           *library.Scheduler
 }
 
-func New(logger *slog.Logger, pool *pgxpool.Pool, scanner ScanTrigger, subCfg subsonic.Config, eventsCfg config.EventsConfig, recCfg config.RecommendationConfig, dataDir string, brandingCfg config.BrandingConfig, coverEnricher *coverart.Enricher, coverArtBackfillCap int, coverSettings *coverart.SettingsService, libraryScanner *library.Scanner, scanCfg library.RunScanConfig) *Server {
-	return &Server{Logger: logger, Pool: pool, Scanner: scanner, SubsonicCfg: subCfg, EventsCfg: eventsCfg, RecommendationCfg: recCfg, DataDir: dataDir, BrandingCfg: brandingCfg, CoverEnricher: coverEnricher, CoverArtBackfillCap: coverArtBackfillCap, CoverSettings: coverSettings, LibraryScanner: libraryScanner, ScanCfg: scanCfg}
+func New(logger *slog.Logger, pool *pgxpool.Pool, scanner ScanTrigger, subCfg subsonic.Config, eventsCfg config.EventsConfig, recCfg config.RecommendationConfig, dataDir string, brandingCfg config.BrandingConfig, coverEnricher *coverart.Enricher, coverArtBackfillCap int, coverSettings *coverart.SettingsService, libraryScanner *library.Scanner, scanCfg library.RunScanConfig, scheduler *library.Scheduler) *Server {
+	return &Server{Logger: logger, Pool: pool, Scanner: scanner, SubsonicCfg: subCfg, EventsCfg: eventsCfg, RecommendationCfg: recCfg, DataDir: dataDir, BrandingCfg: brandingCfg, CoverEnricher: coverEnricher, CoverArtBackfillCap: coverArtBackfillCap, CoverSettings: coverSettings, LibraryScanner: libraryScanner, ScanCfg: scanCfg, Scheduler: scheduler}
 }
 
 func (s *Server) Router() http.Handler {
@@ -114,7 +115,7 @@ func (s *Server) Router() http.Handler {
 		lidarrQuar := lidarrquarantine.NewService(s.Pool, lidarrCfg, lidarrClientFn)
 		tracksSvc := tracks.NewService(s.Pool, s.Logger, lidarrUnmonitorAdapter{fn: lidarrClientFn}, s.DataDir)
 		playlistsSvc := playlists.NewService(s.Pool, s.Logger, s.DataDir)
-		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverArtBackfillCap, s.CoverSettings, s.LibraryScanner, s.ScanCfg, s.DataDir)
+		api.Mount(r, s.Pool, s.Logger, writer, s.RecommendationCfg, lidarrCfg, lidarrReqs, lidarrQuar, tracksSvc, playlistsSvc, s.CoverEnricher, s.CoverArtBackfillCap, s.CoverSettings, s.LibraryScanner, s.ScanCfg, s.Scheduler, s.DataDir)
 		// /api/admin/scan is the only admin route owned by the server package
 		// (it needs the Scanner). Register it as a single inline-middleware
 		// route — using r.Route("/api/admin", ...) here would create a second

internal/server/server_test.go

@@ -24,7 +24,7 @@ import (
 )
 
 func TestHealthz(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -73,7 +73,7 @@ func TestHealthz_IncludesMinClientVersion(t *testing.T) {
 }
 
 func TestRouter_ServesSPAAtRoot(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -92,7 +92,7 @@ func TestRouter_ServesSPAAtRoot(t *testing.T) {
 }
 
 func TestRouter_DeepLinkFallbackReturnsSPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -111,7 +111,7 @@ func TestRouter_DeepLinkFallbackReturnsSPA(t *testing.T) {
 }
 
 func TestRouter_APIPathNotSwallowedBySPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -130,7 +130,7 @@ func TestRouter_APIPathNotSwallowedBySPA(t *testing.T) {
 }
 
 func TestRouter_RestPathNotSwallowedBySPA(t *testing.T) {
-	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), nil, nil, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()
 
@@ -206,7 +206,7 @@ func TestRouter_AdminSubtreeNotShadowed(t *testing.T) {
 	}
 
 	s := New(slog.New(slog.NewTextHandler(io.Discard, nil)), pool,
-		stubScanner{}, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{})
+		stubScanner{}, subsonic.Config{}, config.EventsConfig{}, config.RecommendationConfig{}, "", config.BrandingConfig{}, nil, 0, nil, nil, library.RunScanConfig{}, nil)
 	ts := httptest.NewServer(s.Router())
 	defer ts.Close()