fix: refresh_location_access_scoped_tables trigger fails on multi-row operations

Problem

The refresh_location_access_scoped_tables trigger function fails when multiple rows are deleted/updated in a single transaction. The function creates a temp table _refresh_perms with ON COMMIT DROP, but when called multiple times within the same transaction, it fails with:

ERROR: relation "_refresh_perms" already exists
CONTEXT: SQL statement "CREATE TEMP TABLE _refresh_perms ON COMMIT DROP AS
        SELECT * FROM public.location_access_permission_rows()
        WHERE location_id = ANY(target_location_ids)"
PL/pgSQL function refresh_location_access_scoped_tables(uuid[]) line 33 at SQL statement

Impact

• Cannot delete multiple locations in a single DELETE statement
• Test cleanup fails when multiple test records need to be removed
• Any bulk operations on locations table will fail

Reproduction

DELETE FROM locations WHERE name LIKE 'Test Location%';
-- Fails if more than one row matches

Suggested Fix

Either:

1. Use CREATE TEMP TABLE IF NOT EXISTS and truncate before use
2. Use a unique table name per invocation (e.g., append a random suffix)
3. Drop the table at the end of the function instead of relying on ON COMMIT DROP
4. Use a CTE instead of a temp table

Location

• Function: public.refresh_location_access_scoped_tables(uuid[])
• Migration: 20251219120000_materialize_location_access_scoped_tables.sql