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

src/__tests__/send-log.test.ts

@@ -6,6 +6,7 @@ function createMockDB(): D1Database {
   const insertCols = [
     "ts",
     "route_id",
+    "group_id",
     "event",
     "repo",
     "target",