feat: validate OpenAPI spec using Skooma (#13623)

Adds Skooma-based OpenAPI validation so SDK-facing request specs can
assert that documented request and response contracts match real Rails
behavior. This also upgrades the spec to OpenAPI 3.1 and fixes contract
drift uncovered while validating core application and platform
resources.

Closes
None

Why
We want CI to catch OpenAPI drift before it reaches SDK consumers. While
wiring validation in, this PR surfaced several mismatches between the
documented contract and what the Rails endpoints actually accept or
return.

What this change does
- Adds Skooma-backed OpenAPI validation to the request spec flow and a
dedicated OpenAPI validation spec.
- Migrates nullable schema definitions to OpenAPI 3.1-compatible unions.
- Updates core SDK-facing schemas and payloads across accounts,
contacts, conversations, inboxes, messages, teams, reporting events, and
platform account resources.
- Documents concrete runtime cases that were previously missing or
inaccurate, including nested `profile` update payloads, multipart avatar
uploads, required profile update bodies, nullable inbox feature flags,
and message sender types that include both `Captain::Assistant` and
senderless activity-style messages.
- Regenerates the committed Swagger JSON and tag-group artifacts used by
CI sync checks.

Validation
- `bundle exec rake swagger:build`
- `bundle exec rspec spec/swagger/openapi_spec.rb`

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>

swagger/definitions/request/account/update_payload.yml

@@ -18,20 +18,23 @@ properties:
     example: 'support@example.com'
   # Settings parameters (stored in settings JSONB column)
   auto_resolve_after:
-    type: integer
+    type:
+      - integer
+      - 'null'
     minimum: 10
     maximum: 1439856
-    nullable: true
     description: Auto resolve conversations after specified minutes
     example: 1440
   auto_resolve_message:
-    type: string
-    nullable: true
+    type:
+      - string
+      - 'null'
     description: Message to send when auto resolving
     example: "This conversation has been automatically resolved due to inactivity"
   auto_resolve_ignore_waiting:
-    type: boolean
-    nullable: true
+    type:
+      - boolean
+      - 'null'
     description: Whether to ignore waiting conversations for auto resolve
     example: false
   # Custom attributes parameters (stored in custom_attributes JSONB column)

swagger/definitions/request/conversation/create_payload.yml

@@ -1,7 +1,6 @@
 type: object
 required:
   - source_id
-  - inbox_id
 properties:
   source_id:
     type: string