fix: surface actual Diesel error in store_insight instead of generic InsertError

The previous map_err closures discarded the Diesel error, making
failures like missing columns impossible to diagnose from logs.
Now the underlying error is logged before converting to DbError.

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

src/database/insights_dao.rs

@@ -161,13 +161,13 @@ impl InsightDao for SqliteInsightDao {
             )
             .set(is_current.eq(false))
             .execute(connection.deref_mut())
-            .map_err(|_| anyhow::anyhow!("Update is_current error"))?;
+            .map_err(|e| anyhow::anyhow!("Failed to flip is_current: {}", e))?;
 
             // Insert the new insight as current
             diesel::insert_into(photo_insights)
                 .values(&insight)
                 .execute(connection.deref_mut())
-                .map_err(|_| anyhow::anyhow!("Insert error"))?;
+                .map_err(|e| anyhow::anyhow!("Failed to insert insight: {}", e))?;
 
             // Retrieve the inserted record (is_current = true)
             photo_insights
@@ -175,9 +175,12 @@ impl InsightDao for SqliteInsightDao {
                 .filter(rel_path.eq(&insight.file_path))
                 .filter(is_current.eq(true))
                 .first::<PhotoInsight>(connection.deref_mut())
-                .map_err(|_| anyhow::anyhow!("Query error"))
+                .map_err(|e| anyhow::anyhow!("Failed to retrieve inserted insight: {}", e))
+        })
+        .map_err(|e| {
+            log::error!("store_insight failed: {}", e);
+            DbError::new(DbErrorKind::InsertError)
         })
-        .map_err(|_| DbError::new(DbErrorKind::InsertError))
     }
 
     fn get_insight(