Remove deprecated snapshot system

The register/document model has fully replaced the snapshot system.
Delete every snapshot-scoped row and strip the application code that
referenced them: SnapshotID/SourceID struct fields, snapshot_id IS NULL
filters, snapshot columns from SELECT/INSERT statements and named args,
and the eight migrate-*-snapshots-to-documents one-shot tools.

The remaining snapshot_id / source_id columns, the snapshots and
controls_snapshots tables, the snapshots_type enum, and the
snapshot-scoped indexes are now unused; they are dropped in a follow-up
schema migration so this change can roll back cleanly without leaving
orphaned data.

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

pkg/coredata/migrations/20260506T150405Z.sql

@@ -0,0 +1,30 @@
+-- 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.
+
+-- The register/document model has fully replaced the snapshot system. Delete the
+-- snapshot-scoped data; the schema (snapshot_id / source_id columns, snapshots
+-- table, controls_snapshots, snapshots_type enum, snapshot-scoped indexes) is
+-- dropped in a follow-up migration.
+
+-- processing_activity_vendors stores snapshot_id without an FK to snapshots, so
+-- the cascade delete below would not reach it. Clean it up explicitly first.
+DELETE FROM processing_activity_vendors WHERE snapshot_id IS NOT NULL;
+
+-- Every other table with a snapshot_id has a FOREIGN KEY (snapshot_id) REFERENCES
+-- snapshots(id) ON DELETE CASCADE, so deleting all snapshots removes every
+-- snapshot-scoped row across data, vendors, assets, risks, findings, obligations,
+-- processing_activities, statements_of_applicability, applicability_statements,
+-- the vendor_* sub-tables, the processing_activity DPIA/TIA tables, and the
+-- controls_snapshots junction.
+DELETE FROM snapshots;