feat(who): filter unresolved discussions to open entities only

Workload and active modes now exclude discussions on closed issues and
merged/closed MRs by default. Adds --include-closed flag to restore
the previous behavior when needed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/cli/mod.rs

@@ -964,6 +964,10 @@ pub struct WhoArgs {
     #[arg(long = "include-bots", help_heading = "Scoring")]
     pub include_bots: bool,
 
+    /// Include discussions on closed issues and merged/closed MRs
+    #[arg(long, help_heading = "Filters")]
+    pub include_closed: bool,
+
     /// Remove the default time window (query all history). Conflicts with --since.
     #[arg(
         long = "all-history",