refactor(who): make --limit optional (unlimited default) and fix clippy sort lints

Change the `who` command's --limit flag from default=20 to optional,
so omitting it returns all results. This matches the behavior users
expect when they want a complete expert/workload/active/overlap listing
without an arbitrary cap.

Also applies clippy-recommended sort improvements:
- who/reviews: sort_by(|a,b| b.count.cmp(&a.count)) -> sort_by_key with Reverse
- drift: same pattern for frequency sorting

Adds Theme::color_icon() helper to DRY the stage-icon coloring pattern
used in sync output (was inline closure, now shared method).

src/cli/commands/who/mod.rs

@@ -143,6 +143,8 @@ pub fn run_who(config: &Config, args: &WhoArgs) -> Result<WhoRun> {
         "none"
     };
 
+    let limit = args.limit.map_or(usize::MAX, usize::from);
+
     match mode {
         WhoMode::Expert { path } => {
             // Compute as_of first so --since durations are relative to it.
@@ -159,7 +161,6 @@ pub fn run_who(config: &Config, args: &WhoArgs) -> Result<WhoRun> {
             } else {
                 resolve_since_from(args.since.as_deref(), "24m", as_of_ms)?
             };
-            let limit = usize::from(args.limit);
             let result = expert::query_expert(
                 &conn,
                 &path,
@@ -191,7 +192,7 @@ pub fn run_who(config: &Config, args: &WhoArgs) -> Result<WhoRun> {
                 .as_deref()
                 .map(resolve_since_required)
                 .transpose()?;
-            let limit = usize::from(args.limit);
+
             let result = workload::query_workload(
                 &conn,
                 username,
@@ -231,7 +232,7 @@ pub fn run_who(config: &Config, args: &WhoArgs) -> Result<WhoRun> {
         }
         WhoMode::Active => {
             let since_ms = resolve_since(args.since.as_deref(), "7d")?;
-            let limit = usize::from(args.limit);
+
             let result =
                 active::query_active(&conn, project_id, since_ms, limit, args.include_closed)?;
             Ok(WhoRun {
@@ -249,7 +250,7 @@ pub fn run_who(config: &Config, args: &WhoArgs) -> Result<WhoRun> {
         }
         WhoMode::Overlap { path } => {
             let since_ms = resolve_since(args.since.as_deref(), "30d")?;
-            let limit = usize::from(args.limit);
+
             let result = overlap::query_overlap(&conn, &path, project_id, since_ms, limit)?;
             Ok(WhoRun {
                 resolved_input: WhoResolvedInput {