feat(daemon): add auto-scan, force start, and stall timeout default

- Auto-scan: daemon scans library daily (configurable via config.toml)
  [library] auto_scan = true, scan_interval = "24h"
- Force start: tasks with forceStart=true bypass concurrency semaphore
  (like Transmission's Force Start — opens temporary extra slot)
- Stall timeout default: 30m instead of unlimited, prevents dead torrents
  from permanently blocking download slots
- ForceStart field in agent.Task for CLI/server communication

internal/agent/types.go

@@ -70,6 +70,7 @@ type Task struct {
 	NzbPassword     string `json:"nzbPassword,omitempty"`    // Password for encrypted NZB archives
 	ReplacePath     string `json:"replacePath,omitempty"`    // File to replace after download (upgrade mode)
 	LibraryItemID   int    `json:"libraryItemId,omitempty"`  // Library item being upgraded
+	ForceStart      bool   `json:"forceStart,omitempty"`     // Bypass queue (like Transmission's Force Start)
 }
 
 // TasksResponse wraps the array of tasks returned by the server.