fix: allow duplicate route IDs across groups and add group_id to send_logs

- Change validateRoutes to per-group ID uniqueness instead of global
- Remove post-merge cross-group route ID uniqueness checks
- Include groupId in msg:* KV key to prevent collision
- Add group_id column to send_logs table (migration 0004)
- Record groupId in send_logs for accurate permission filtering
- Use groupId from log entries for admin log access checks

migrations/0004_add_group_id.sql

@@ -0,0 +1 @@
+ALTER TABLE send_logs ADD COLUMN group_id TEXT;