Let users pick and order their workbench module tiles.

Per-user layout lives in the new app_user.prefs JSON column, read via
/v1/auth/me and written via PUT /v1/auth/me/prefs/workbench. The
workbench gets an in-place edit mode (gear -> drag to reorder, x to
remove, tray to add back, reset/done). Reset stores empty prefs so
registry changes still apply; ids of modules the user can't currently
see are kept on save.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

alembic/versions/20261013_user_prefs.py

@@ -0,0 +1,52 @@
+"""Add app_user.prefs JSON for per-user UI preferences.
+
+Revision ID: 20261013_user_prefs
+Revises: 20260922_biz_state_queued
+Create Date: 2026-10-13
+"""
+
+from __future__ import annotations
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "20261013_user_prefs"
+down_revision: Union[str, Sequence[str], None] = "20260922_biz_state_queued"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    bind = op.get_bind()
+    dialect = str(getattr(bind.dialect, "name", "") or "").lower()
+    if dialect.startswith("postgres"):
+        op.execute(
+            "ALTER TABLE app_user ADD COLUMN IF NOT EXISTS prefs JSON DEFAULT '{}'::json NOT NULL"
+        )
+        # Ensure NOT NULL + default for brownfield rows that already had a nullable column.
+        op.execute("UPDATE app_user SET prefs = '{}'::json WHERE prefs IS NULL")
+        op.execute("ALTER TABLE app_user ALTER COLUMN prefs SET DEFAULT '{}'::json")
+        op.execute("ALTER TABLE app_user ALTER COLUMN prefs SET NOT NULL")
+    else:
+        insp = sa.inspect(bind)
+        if "app_user" in insp.get_table_names():
+            cols = {c["name"] for c in insp.get_columns("app_user")}
+            if "prefs" not in cols:
+                op.add_column(
+                    "app_user",
+                    sa.Column("prefs", sa.JSON(), nullable=False, server_default="{}"),
+                )
+
+
+def downgrade() -> None:
+    bind = op.get_bind()
+    dialect = str(getattr(bind.dialect, "name", "") or "").lower()
+    if dialect.startswith("postgres"):
+        op.execute("ALTER TABLE app_user DROP COLUMN IF EXISTS prefs")
+    else:
+        try:
+            op.drop_column("app_user", "prefs")
+        except Exception:
+            pass