add --state-dir (-D) flag to persist enabled/logs/pid across reboots

socket stays in /tmp/rss/rss.sock so client commands need no extra args;
state dir is controlled by RSS_STATE_DIR or --state-dir and stores
enabled flags, logs, and daemon.pid in a persistent location.

src/cli.rs

@@ -6,6 +6,9 @@ pub struct Cli {
     #[arg(short = 'C', long, global = true, help = "Path to config file")]
     pub config: Option<String>,
 
+    #[arg(short = 'D', long, global = true, help = "Path to state directory (default: /tmp/rss or $RSS_STATE_DIR)")]
+    pub state_dir: Option<String>,
+
     #[command(subcommand)]
     pub command: Commands,
 }

src/main.rs

@@ -15,6 +15,10 @@ use std::sync::atomic::{AtomicBool, Ordering};
 fn main() {
     let cli = Cli::parse();
 
+    if let Some(ref dir) = cli.state_dir {
+        std::env::set_var("RSS_STATE_DIR", dir);
+    }
+
     match cli.command {
         Commands::Daemon => {
             let config_path = resolve_config_path(cli.config.as_deref());