insight-chat: code-review polish on the tool-gating PR

- search_messages now delegates to search_messages_with_contact(.., None)
  so the two methods share a single HTTP path. Drops the dead-code
  warning and the ~30-line duplication.
- DailySummaryDao gains has_any_summaries (LIMIT 1 existence probe)
  used by current_gate_opts; the SELECT COUNT(*) get_total_summary_count
  added in the prior commit is removed (it had no other caller).
- current_gate_opts doc comment corrected to describe what the probes
  actually do.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/database/daily_summary_dao.rs

@@ -76,12 +76,13 @@ pub trait DailySummaryDao: Sync + Send {
         contact: &str,
     ) -> Result<i64, DbError>;
 
-    /// Get total count of all summaries (across all contacts). Used by
-    /// `current_gate_opts` to check whether daily_summaries are present.
-    fn get_total_summary_count(
+    /// Cheap presence check — returns true iff at least one daily summary row
+    /// exists. Used by gating logic that only needs "is the table empty?",
+    /// avoiding a `COUNT(*)` full scan on large corpora.
+    fn has_any_summaries(
         &mut self,
         context: &opentelemetry::Context,
-    ) -> Result<i64, DbError>;
+    ) -> Result<bool, DbError>;
 }
 
 pub struct SqliteDailySummaryDao {
@@ -462,20 +463,27 @@ impl DailySummaryDao for SqliteDailySummaryDao {
         .map_err(|_| DbError::new(DbErrorKind::QueryError))
     }
 
-    fn get_total_summary_count(
-        &mut self,
-        context: &opentelemetry::Context,
-    ) -> Result<i64, DbError> {
-        trace_db_call(context, "query", "get_total_summary_count", |_span| {
+    fn has_any_summaries(&mut self, context: &opentelemetry::Context) -> Result<bool, DbError> {
+        trace_db_call(context, "query", "has_any_summaries", |_span| {
             let mut conn = self
                 .connection
                 .lock()
                 .expect("Unable to get DailySummaryDao");
 
-            diesel::sql_query("SELECT COUNT(*) as count FROM daily_conversation_summaries")
-                .get_result::<CountResult>(conn.deref_mut())
-                .map(|r| r.count)
-                .map_err(|e| anyhow::anyhow!("Count query error: {:?}", e))
+            #[derive(QueryableByName)]
+            struct ProbeResult {
+                #[diesel(sql_type = diesel::sql_types::Integer)]
+                #[allow(dead_code)]
+                one: i32,
+            }
+
+            let rows: Vec<ProbeResult> = diesel::sql_query(
+                "SELECT 1 as one FROM daily_conversation_summaries LIMIT 1",
+            )
+            .load(conn.deref_mut())
+            .map_err(|e| anyhow::anyhow!("Failed to probe daily summaries: {}", e))?;
+
+            Ok(!rows.is_empty())
         })
         .map_err(|_| DbError::new(DbErrorKind::QueryError))
     }