feat: add job management subcommand 🎮

Add `paracas job` subcommand for managing background downloads:
- pause: suspend a running job with SIGSTOP
- resume: continue a paused job with SIGCONT (respawns if needed)
- kill: terminate a job with SIGTERM/SIGKILL
- clean: remove finished jobs from storage

Also show help menu when no subcommand is provided.

crates/paracas-daemon/src/job.rs

@@ -17,6 +17,8 @@ pub enum JobStatus {
     Pending,
     /// Job is currently running.
     Running,
+    /// Job is paused by the user.
+    Paused,
     /// Job completed successfully.
     Completed,
     /// Job failed with an error.
@@ -38,6 +40,7 @@ impl JobStatus {
         match self {
             Self::Pending => "pending",
             Self::Running => "running",
+            Self::Paused => "paused",
             Self::Completed => "completed",
             Self::Failed => "failed",
             Self::Cancelled => "cancelled",
@@ -217,6 +220,31 @@ impl DownloadJob {
             }
         }
     }
+
+    /// Marks the job as paused.
+    pub fn mark_paused(&mut self) {
+        self.status = JobStatus::Paused;
+
+        // Pause any running tasks
+        for task in &mut self.tasks {
+            if task.status == JobStatus::Running {
+                task.status = JobStatus::Paused;
+            }
+        }
+    }
+
+    /// Marks the job as resumed (back to running).
+    pub fn mark_resumed(&mut self, pid: u32) {
+        self.status = JobStatus::Running;
+        self.pid = Some(pid);
+
+        // Resume any paused tasks
+        for task in &mut self.tasks {
+            if task.status == JobStatus::Paused {
+                task.status = JobStatus::Running;
+            }
+        }
+    }
 }
 
 #[cfg(test)]