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>

packages/webhook-notifier/manifest.json

@@ -30,7 +30,6 @@
         "ordinal": 0,
         "stage_mode": "form",
         "audience": "team",
-        "stage_type": "simple",
         "auto_transition": false,
         "form_template": {
           "fieldsets": [
@@ -50,16 +49,14 @@
         "ordinal": 1,
         "stage_mode": "automated",
         "audience": "system",
-        "stage_type": "automated",
         "auto_transition": true,
         "starlark_hook": "webhook-notifier:on_fire"
       },
       {
         "name": "result",
         "ordinal": 2,
-        "stage_mode": "review",
+        "stage_mode": "form",
         "audience": "team",
-        "stage_type": "simple",
         "auto_transition": false,
         "form_template": {
           "fieldsets": [