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

docs/API.md

@@ -660,7 +660,10 @@ Return current application configuration.
     "data_dir": "data",
     "scheduler": {
         "enabled": true,
-        "interval_minutes": 60
+        "interval_minutes": 60,
+        "schedule_time": "03:00",
+        "schedule_days": ["mon", "tue", "wed", "thu", "fri", "sat", "sun"],
+        "auto_download_after_rescan": false
     },
     "logging": {
         "level": "INFO",
@@ -691,7 +694,9 @@ Apply an update to the configuration.
 {
     "scheduler": {
         "enabled": true,
-        "interval_minutes": 30
+        "interval_minutes": 60,
+        "schedule_time": "06:30",
+        "schedule_days": ["mon", "wed", "fri"]
     },
     "logging": {
         "level": "DEBUG"
@@ -1177,47 +1182,21 @@ Source: [src/server/api/nfo.py](../src/server/api/nfo.py#L637-L684)
 
 Prefix: `/api/scheduler`
 
-Source: [src/server/api/scheduler.py](../src/server/api/scheduler.py#L1-L122)
+All GET/POST config responses share the same envelope:
+
+```json
+{
+    "success": true,
+    "config": { ... },
+    "status": { ... }
+}
+```
+
+Source: [src/server/api/scheduler.py](../src/server/api/scheduler.py)
 
 ### GET /api/scheduler/config
 
-Get current scheduler configuration.
-
-**Authentication:** Required
-
-**Response (200 OK):**
-
-```json
-{
-    "enabled": true,
-    "interval_minutes": 60
-}
-```
-
-Source: [src/server/api/scheduler.py](../src/server/api/scheduler.py#L22-L42)
-
-### POST /api/scheduler/config
-
-Update scheduler configuration.
-
-**Authentication:** Required
-
-**Request Body:**
-
-```json
-{
-    "enabled": true,
-    "interval_minutes": 30
-}
-```
-
-**Response (200 OK):** Updated scheduler configuration
-
-Source: [src/server/api/scheduler.py](../src/server/api/scheduler.py#L45-L75)
-
-### POST /api/scheduler/trigger-rescan
-
-Manually trigger a library rescan.
+Get current scheduler configuration and runtime status.
 
 **Authentication:** Required
 
@@ -1226,11 +1205,65 @@ Manually trigger a library rescan.
 ```json
 {
     "success": true,
+    "config": {
+        "enabled": true,
+        "interval_minutes": 60,
+        "schedule_time": "03:00",
+        "schedule_days": ["mon", "tue", "wed", "thu", "fri", "sat", "sun"],
+        "auto_download_after_rescan": false
+    },
+    "status": {
+        "is_running": true,
+        "next_run": "2025-07-15T03:00:00+00:00",
+        "last_run": null,
+        "scan_in_progress": false
+    }
+}
+```
+
+### POST /api/scheduler/config
+
+Update scheduler configuration and apply changes immediately.
+
+**Authentication:** Required
+
+**Request Body (all fields optional, uses model defaults):**
+
+```json
+{
+    "enabled": true,
+    "schedule_time": "06:30",
+    "schedule_days": ["mon", "wed", "fri"],
+    "auto_download_after_rescan": true
+}
+```
+
+**Response (200 OK):** Same envelope as GET, reflecting saved values.
+
+**Validation errors (422):**
+
+- `schedule_time` must match `HH:MM` (00:00–23:59)
+- `schedule_days` entries must be one of `mon tue wed thu fri sat sun`
+- `interval_minutes` must be ≥ 1
+
+### POST /api/scheduler/trigger-rescan
+
+Manually trigger a library rescan (and auto-download if configured).
+
+**Authentication:** Required
+
+**Response (200 OK):**
+
+```json
+{
     "message": "Rescan started successfully"
 }
 ```
 
-Source: [src/server/api/scheduler.py](../src/server/api/scheduler.py#L78-L122)
+**Error responses:**
+
+- `503` — SeriesApp not yet initialised
+- `500` — Rescan failed unexpectedly
 
 ---