fix: make gateway migrations idempotent + self-heal drizzle history

Prevent recurring infinite restart loop (389x crash) caused by drizzle
re-applying already-applied migrations when public.__drizzle_migrations
tracking is empty/partial.

- 0017/0018: ADD COLUMN IF NOT EXISTS (re-run safe)
- 0019: DO-block rename that handles all prior states (server_name-only,
  both columns, or server_nick-only) so it never errors or double-renames
- seedDrizzleHistory: reconcile tracked created_at to the journal's latest
  'when' when the schema already reflects the latest migration, instead of
  early-returning on an existing-but-empty/partial tracking table

services/discord-gateway/drizzle/migrations/0017_add_username_to_moderation_actions.sql

@@ -1,4 +1,4 @@
-ALTER TABLE "moderation_actions" ADD COLUMN "username" text;
+ALTER TABLE "moderation_actions" ADD COLUMN IF NOT EXISTS "username" text;
 --> statement-breakpoint
 -- Backfill username from messages table for existing actions
 UPDATE "moderation_actions" a

services/discord-gateway/drizzle/migrations/0018_add_server_name_to_moderation_actions.sql

@@ -1 +1 @@
-ALTER TABLE "moderation_actions" ADD COLUMN "server_name" text;
+ALTER TABLE "moderation_actions" ADD COLUMN IF NOT EXISTS "server_name" text;

services/discord-gateway/drizzle/migrations/0019_rename_server_name_to_server_nick.sql

@@ -1,4 +1,26 @@
 -- Rename server_name (guild name) -> server_nick (member's server nickname)
 -- server_name was added in 0018 but never populated (all NULL), so renaming
 -- the empty column is safe and keeps retention semantics correct.
-ALTER TABLE "moderation_actions" RENAME COLUMN "server_name" TO "server_nick";
+-- Idempotent across all possible prior states:
+--   • server_name present, server_nick absent  -> rename
+--   • both present (backfill created server_nick) -> drop the stale server_name
+--   • server_nick present only                -> already done, no-op
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM information_schema.columns
+    WHERE table_name = 'moderation_actions' AND column_name = 'server_name'
+  ) AND NOT EXISTS (
+    SELECT 1 FROM information_schema.columns
+    WHERE table_name = 'moderation_actions' AND column_name = 'server_nick'
+  ) THEN
+    ALTER TABLE "moderation_actions" RENAME COLUMN "server_name" TO "server_nick";
+  ELSIF EXISTS (
+    SELECT 1 FROM information_schema.columns
+    WHERE table_name = 'moderation_actions' AND column_name = 'server_name'
+  ) THEN
+    -- server_nick already exists (e.g. backfilled out-of-band) — drop the
+    -- now-redundant server_name column instead of renaming into a conflict.
+    ALTER TABLE "moderation_actions" DROP COLUMN "server_name";
+  END IF;
+END $$;