fix(translate): add missing target_languages column to production DB

Migration 2a7b8c9d0e1f adds target_languages (JSON) to translation_jobs.
Uses ADD COLUMN IF NOT EXISTS for idempotent PostgreSQL deployment.

Fixes 500 error on GET /api/translate/jobs:
  column translation_jobs.target_languages does not exist

Migration chain is now clean: 5 linear revisions, no orphans.

backend/alembic/versions/2a7b8c9d0e1f_add_target_languages_to_translation_jobs.py

@@ -0,0 +1,67 @@
+"""Add target_languages column to translation_jobs (multi-language support)
+
+Revision ID: 2a7b8c9d0e1f
+Revises: 8dd0a93af539
+Create Date: 2026-05-14 23:55:00.000000
+
+"""
+from collections.abc import Sequence
+
+import sqlalchemy as sa
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision: str = "2a7b8c9d0e1f"
+down_revision: str | Sequence[str] | None = "8dd0a93af539"
+branch_labels: str | Sequence[str] | None = None
+depends_on: str | Sequence[str] | None = None
+
+
+def upgrade() -> None:
+    """Add target_languages column to translation_jobs.
+
+    Production PostgreSQL may be missing this column if the initial
+    migration (ed310b33f02c) was applied from a version that predated
+    the multi-language support feature.  This migration safely adds it
+    with IF NOT EXISTS on PostgreSQL, and handles SQLite explicitly.
+    """
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    columns = [c["name"] for c in inspector.get_columns("translation_jobs")]
+
+    if "target_languages" in columns:
+        # Column already exists — nothing to do
+        return
+
+    if bind.engine.name == "sqlite":
+        op.add_column(
+            "translation_jobs",
+            sa.Column(
+                "target_languages",
+                sa.JSON(),
+                nullable=True,
+                comment="List of BCP-47 target language codes (multi-language support)",
+            ),
+        )
+    else:
+        # PostgreSQL and others: use IF NOT EXISTS for safety
+        op.execute(
+            "ALTER TABLE translation_jobs "
+            "ADD COLUMN IF NOT EXISTS target_languages JSON "
+            "DEFAULT NULL"
+        )
+
+
+def downgrade() -> None:
+    """Drop target_languages column from translation_jobs."""
+    bind = op.get_bind()
+    if bind.engine.name == "sqlite":
+        inspector = sa.inspect(bind)
+        columns = [c["name"] for c in inspector.get_columns("translation_jobs")]
+        if "target_languages" in columns:
+            op.drop_column("translation_jobs", "target_languages")
+    else:
+        op.execute(
+            "ALTER TABLE translation_jobs DROP COLUMN IF EXISTS target_languages"
+        )