feat(rust): dlp --since — filter URLs by message timestamp

Rust-only extension (no python counterpart): --since 5d / 12h / 2026-10-04
keeps only URLs posted at/after the cutoff. URLs without a timestamp
(e.g. --urls-file lists) are kept with a warning.

version-rust/src/main.rs

@@ -90,6 +90,9 @@ struct DlpArgs {
     /// process only one host class
     #[arg(long)]
     only: Option<String>,
+    /// only URLs posted at/after this point: e.g. 5d, 12h, 2026-10-04
+    #[arg(long, value_name = "WHEN")]
+    since: Option<String>,
     /// download at most N pending URLs per host class (test runs)
     #[arg(long, value_name = "N")]
     limit: Option<usize>,
@@ -343,6 +346,7 @@ impl From<&DlpArgs> for orchestrate::RunOpts {
             limit: a.limit,
             shuffle: a.shuffle,
             only: a.only.clone(),
+            since: a.since.clone(),
             dry_run: a.dry_run,
             fresh: a.fresh,
         }