feat: cron-based scheduler with auto-download after rescan

- Replace asyncio sleep loop with APScheduler AsyncIOScheduler + CronTrigger
- Add schedule_time (HH:MM), schedule_days (days of week), auto_download_after_rescan fields to SchedulerConfig
- Add _auto_download_missing() to queue missing episodes after rescan
- Reload config live via reload_config(SchedulerConfig) without restart
- Update GET/POST /api/scheduler/config to return {success, config, status} envelope
- Add day-of-week pill toggles to Settings -> Scheduler section in UI
- Update JS loadSchedulerConfig / saveSchedulerConfig for new API shape
- Add 29 unit tests for SchedulerConfig model, 18 unit tests for SchedulerService
- Rewrite 23 endpoint tests and 36 integration tests for APScheduler behaviour
- Coverage: 96% api/scheduler, 95% scheduler_service, 90% total (>= 80% threshold)
- Update docs: API.md, CONFIGURATION.md, features.md, CHANGELOG.md

src/server/web/static/css/pages/index.css

@@ -228,3 +228,122 @@
     font-size: var(--font-size-title);
   }
 }
+
+/* ============================================================
+   Scheduler day-of-week toggle pills
+   ============================================================ */
+
+.scheduler-days-container {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--spacing-sm);
+  margin-top: var(--spacing-sm);
+}
+
+.scheduler-day-toggle-label {
+  display: inline-flex;
+  align-items: center;
+  cursor: pointer;
+  user-select: none;
+}
+
+/* Hide the raw checkbox visually */
+.scheduler-day-toggle-label .scheduler-day-checkbox {
+  position: absolute;
+  opacity: 0;
+  width: 0;
+  height: 0;
+}
+
+/* Pill styling */
+.scheduler-day-label {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  min-width: 2.6rem;
+  padding: var(--spacing-xs) var(--spacing-sm);
+  border: 1px solid var(--color-border);
+  border-radius: var(--border-radius-xl);
+  font-size: var(--font-size-caption);
+  font-weight: 600;
+  color: var(--color-text-secondary);
+  background-color: var(--color-bg-secondary);
+  transition: background-color var(--transition-duration) var(--transition-easing),
+              color var(--transition-duration) var(--transition-easing),
+              border-color var(--transition-duration) var(--transition-easing);
+  cursor: pointer;
+}
+
+/* Checked state – filled accent */
+.scheduler-day-checkbox:checked + .scheduler-day-label {
+  background-color: var(--color-accent);
+  border-color: var(--color-accent);
+  color: #ffffff;
+}
+
+/* Hover for unchecked */
+.scheduler-day-toggle-label:hover .scheduler-day-label {
+  border-color: var(--color-accent);
+  color: var(--color-accent);
+}
+
+/* Hover for checked */
+.scheduler-day-toggle-label:hover .scheduler-day-checkbox:checked + .scheduler-day-label {
+  background-color: var(--color-accent-hover);
+  border-color: var(--color-accent-hover);
+  color: #ffffff;
+}
+
+/* Dark theme overrides */
+[data-theme="dark"] .scheduler-day-label {
+  border-color: var(--color-border-dark);
+  color: var(--color-text-secondary-dark);
+  background-color: var(--color-bg-secondary-dark);
+}
+
+[data-theme="dark"] .scheduler-day-checkbox:checked + .scheduler-day-label {
+  background-color: var(--color-accent-dark);
+  border-color: var(--color-accent-dark);
+  color: var(--color-bg-primary-dark);
+}
+
+[data-theme="dark"] .scheduler-day-toggle-label:hover .scheduler-day-label {
+  border-color: var(--color-accent-dark);
+  color: var(--color-accent-dark);
+}
+
+/* Next run display */
+#scheduler-next-run {
+  font-style: italic;
+  font-size: var(--font-size-caption);
+  color: var(--color-text-tertiary);
+}
+
+[data-theme="dark"] #scheduler-next-run {
+  color: var(--color-text-tertiary-dark);
+}
+
+/* Advanced/collapsible section */
+.config-advanced {
+  font-size: var(--font-size-caption);
+  color: var(--color-text-secondary);
+  margin-top: var(--spacing-sm);
+}
+
+.config-advanced summary {
+  cursor: pointer;
+  padding: var(--spacing-xs) 0;
+  font-weight: 500;
+}
+
+/* Responsive: wrap day pills to 2 rows on mobile */
+@media (max-width: 480px) {
+  .scheduler-days-container {
+    gap: var(--spacing-xs);
+  }
+
+  .scheduler-day-label {
+    min-width: 2.2rem;
+    padding: var(--spacing-xs);
+  }
+}