Feat v0.9.6 deprecate stage_type, collapse stage_mode

stage_type no longer validated — starlark_hook presence determines
automation. stage_mode collapsed from 4→3 values (form/delegated/
automated); "review" mapped to "form" on input for backward compat.
Migration 018 converts existing rows. Review surface removed (~110
lines). 4 package manifests updated.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/database/migrations/postgres/018_stage_mode_collapse.sql

@@ -0,0 +1,13 @@
+-- Armature — 018 Stage Mode Collapse
+-- Deprecate stage_type validation. Collapse stage_mode: review → form.
+
+-- 1. Migrate existing review rows to form
+UPDATE workflow_stages SET stage_mode = 'form' WHERE stage_mode = 'review';
+
+-- 2. Replace CHECK constraint on stage_mode (drop review)
+ALTER TABLE workflow_stages DROP CONSTRAINT IF EXISTS workflow_stages_stage_mode_check;
+ALTER TABLE workflow_stages ADD CONSTRAINT workflow_stages_stage_mode_check
+    CHECK (stage_mode IN ('form', 'delegated', 'automated'));
+
+-- 3. Drop CHECK constraint on stage_type (any value accepted)
+ALTER TABLE workflow_stages DROP CONSTRAINT IF EXISTS workflow_stages_stage_type_check;