Drop dead users_organizations table and unused columns

Remove schema objects that are no longer referenced by any query code,
GraphQL resolver, or frontend and only survive in old migration files:

- users_organizations: superseded by iam_memberships (data was migrated in
  20251006T220024Z).
- organizations.logo_object_key: pre-files-table logo storage; replaced by
  logo_file_id / horizontal_logo_file_id (data migrated in 20251009T140000Z).
- trust_center_accesses.has_accepted_non_disclosure_agreement,
  has_accepted_non_disclosure_agreement_metadata, nda_file_id and
  last_token_expires_at: the NDA-acceptance flow now uses
  electronic_signature_id together with the state column.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/coredata/migrations/20260602T141500Z.sql

@@ -0,0 +1,37 @@
+-- Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+--
+-- Permission to use, copy, modify, and/or distribute this software for any
+-- purpose with or without fee is hereby granted, provided that the above
+-- copyright notice and this permission notice appear in all copies.
+--
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+-- REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+-- AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+-- INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+-- LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+-- OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+-- PERFORMANCE OF THIS SOFTWARE.
+
+-- Drop dead schema left over from completed migrations. None of the objects
+-- below are referenced by any query code, GraphQL resolver, or frontend; they
+-- only appear in older migration files.
+
+-- users_organizations was superseded by iam_memberships (data was copied over
+-- in 20251006T220024Z). The legacy junction table is no longer read or written.
+DROP TABLE users_organizations;
+
+-- organizations.logo_object_key is the pre-files-table logo storage. Its data
+-- was migrated into the files table (20251009T140000Z) and the application now
+-- uses logo_file_id / horizontal_logo_file_id instead.
+ALTER TABLE organizations
+    DROP COLUMN logo_object_key;
+
+-- The trust center NDA-acceptance flow now records acceptance through
+-- electronic_signature_id together with the state column. The original boolean
+-- flag, its metadata, the standalone NDA file reference, and the token expiry
+-- column are all unused.
+ALTER TABLE trust_center_accesses
+    DROP COLUMN has_accepted_non_disclosure_agreement,
+    DROP COLUMN has_accepted_non_disclosure_agreement_metadata,
+    DROP COLUMN nda_file_id,
+    DROP COLUMN last_token_expires_at;