feat(me): add 30-day mention age cutoff to filter stale @-mentions

Previously, query_mentioned_in returned mentions from any time in the
entity's history as long as the entity was still open (or recently closed).
This caused noise: a mention from 6 months ago on a still-open issue would
appear in the dashboard indefinitely.

Now the SQL filters notes by created_at > mention_cutoff_ms, defaulting to
30 days. The recency_cutoff (7 days) still governs closed/merged entity
visibility — this new cutoff governs mention note age on open entities.

Signature change: query_mentioned_in gains a mention_cutoff_ms parameter.
All existing test call sites updated. Two new tests verify the boundary:
- mentioned_in_excludes_old_mention_on_open_issue (45-day mention filtered)
- mentioned_in_includes_recent_mention_on_open_issue (5-day mention kept)

src/cli/commands/me/mod.rs

@@ -27,6 +27,8 @@ const DEFAULT_ACTIVITY_SINCE_DAYS: i64 = 1;
 const MS_PER_DAY: i64 = 24 * 60 * 60 * 1000;
 /// Recency window for closed/merged items in the "Mentioned In" section: 7 days.
 const RECENCY_WINDOW_MS: i64 = 7 * MS_PER_DAY;
+/// Only show mentions from notes created within this window (30 days).
+const MENTION_WINDOW_MS: i64 = 30 * MS_PER_DAY;
 
 /// Resolve the effective username from CLI flag or config.
 ///
@@ -151,7 +153,14 @@ pub fn run_me(config: &Config, args: &MeArgs, robot_mode: bool) -> Result<()> {
 
     let mentioned_in = if want_mentions {
         let recency_cutoff = crate::core::time::now_ms() - RECENCY_WINDOW_MS;
-        query_mentioned_in(&conn, username, &project_ids, recency_cutoff)?
+        let mention_cutoff = crate::core::time::now_ms() - MENTION_WINDOW_MS;
+        query_mentioned_in(
+            &conn,
+            username,
+            &project_ids,
+            recency_cutoff,
+            mention_cutoff,
+        )?
     } else {
         Vec::new()
     };