chore(db): drop orphaned import_* columns from user_table_definitions (#7188)

Contract phase for the table-jobs cutover. Migration 0233 moved import job
state into table_jobs and removed every application read and write, but
deliberately left the five import_* columns in place so the then-deployed app
version kept working across blue/green cutover. The follow-up drop was never
written.

The columns have been invisible to Drizzle ever since: the model lost them in
the same release, so every meta snapshot from 0233 onward already omits them
and `drizzle-kit generate` reports no diff. They exist only physically, which
is why this is a custom migration.

Author: waleedlatif1

packages/db/migrations/0310_drop_orphaned_table_import_columns.sql

@@ -0,0 +1,33 @@
+-- Custom SQL migration file, put your code below! --
+
+-- Contract of #4915 (migration 0233), which moved import job state out of these five
+-- `user_table_definitions` columns into `table_jobs` and removed every application read
+-- and write in the same release. 0233 deferred the drop on purpose so the then-deployed
+-- app version could keep using the columns across blue/green cutover; that deploy drained
+-- long ago (0233 is 77 migrations back). The deferral was never recorded with a
+-- `contract-pending` marker, which is why it went unnoticed.
+--
+-- This is a custom migration because Drizzle cannot generate it: #4915 removed the fields
+-- from `schema.ts` in the same release, so every meta snapshot from 0233 onward already
+-- omits them. `drizzle-kit generate` diffs schema-vs-snapshot, never schema-vs-database,
+-- and reports "No schema changes, nothing to migrate" — the columns exist only physically.
+--
+-- Verified before writing: zero references to any of the five names (snake_case or
+-- camelCase) anywhere outside packages/db/migrations, and in production all five are empty
+-- across all 42,394 `user_table_definitions` rows.
+--
+-- One statement, not five: each ALTER takes its own ACCESS EXCLUSIVE lock on a write-hot
+-- relation, and the runner retries the whole file on lock_timeout (5s, 8 attempts). A single
+-- statement means one lock acquisition and no partially-dropped state between retries. Each
+-- clause is IF EXISTS so the replay is a no-op. No CASCADE on purpose — nothing depends on
+-- these columns (verified: no index, constraint, view, rule, trigger, function, publication,
+-- or generated column references them in production), so if that ever changed this would
+-- fail loudly instead of silently dropping the dependent object.
+
+-- migration-safe: contract of #4915 — the last readers/writers were removed there and 0233 backfilled the data into table_jobs; 0 refs remain anywhere in apps/ or packages/, and all five columns are empty across all 42,394 production rows
+ALTER TABLE "user_table_definitions"
+	DROP COLUMN IF EXISTS "import_status",
+	DROP COLUMN IF EXISTS "import_id",
+	DROP COLUMN IF EXISTS "import_error",
+	DROP COLUMN IF EXISTS "import_rows_processed",
+	DROP COLUMN IF EXISTS "import_started_at";