Use runtime pool check instead of Mix.env for migration

Mix.env() is not available in production releases, so we need to check
the repo's pool configuration at runtime instead. In test, the pool is
Ecto.Adapters.SQL.Sandbox which doesn't support CONCURRENTLY, so we
skip index creation. In production/dev, indexes are created normally.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

priv/repo/migrations/20251025183718_add_callsign_search_indexes.exs

@@ -1,10 +1,19 @@
 defmodule Aprsme.Repo.Migrations.AddCallsignSearchIndexes do
   use Ecto.Migration
+  @disable_ddl_transaction true
+  @disable_migration_lock true
 
   def up do
-    # In test environment, skip index creation to avoid timeout issues
-    # Indexes will be created in production where the table has actual data
-    if Mix.env() != :test do
+    # Check if we're in a test environment by looking at the repo config
+    # In test, the pool is Ecto.Adapters.SQL.Sandbox which doesn't support CONCURRENTLY
+    pool_module = Aprsme.Repo.config()[:pool]
+
+    if pool_module == Ecto.Adapters.SQL.Sandbox do
+      # Test environment - skip index creation to avoid timeout issues
+      # The test database is empty anyway
+      :ok
+    else
+      # Production/dev environment - create indexes with CONCURRENTLY
       # Add index on sender for pattern matching searches
       # Using text_pattern_ops for LIKE/ILIKE queries via raw SQL
       execute """