Move document classification from document to document version

Classification now lives exclusively on DocumentVersion. The field is
removed from the Document model, all SQL queries, GraphQL Document
type, SignableDocument type, UpdateDocumentInput, and MCP Document
schema.

New documents still accept classification in CreateDocumentInput,
applied to the first version. New drafts inherit classification from
the previous version. PDF generation uses the version classification.

The drawer allows editing classification on draft versions via the
updateDocumentVersion mutation. Classification is read-only on
published versions.

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

pkg/server/api/mcp/v1/specification.yaml

@@ -5186,7 +5186,6 @@ components:
         - organization_id
         - title
         - document_type
-        - classification
         - trust_center_visibility
         - status
         - created_at
@@ -5204,9 +5203,6 @@ components:
         document_type:
           $ref: "#/components/schemas/DocumentType"
           description: Document type
-        classification:
-          $ref: "#/components/schemas/DocumentClassification"
-          description: Document classification
         current_published_major:
           type:
             - integer
@@ -5459,9 +5455,6 @@ components:
         title:
           type: string
           description: Document title
-        classification:
-          $ref: "#/components/schemas/DocumentClassification"
-          description: Document classification
         document_type:
           $ref: "#/components/schemas/DocumentType"
           description: Document type
@@ -5580,7 +5573,6 @@ components:
       type: object
       required:
         - document_version_id
-        - content
       properties:
         document_version_id:
           $ref: "#/components/schemas/GID"
@@ -5588,6 +5580,9 @@ components:
         content:
           type: string
           description: Document content
+        classification:
+          $ref: "#/components/schemas/DocumentClassification"
+          description: Document classification
 
     UpdateDocumentVersionOutput:
       type: object