Add document approval workflow

Introduce a complete approval system for document publishing. Document
versions can now require approval from selected reviewers before being
published, with automatic publishing once all approvers have approved.

- Add approval quorum and decision tables with backfill migration
- Implement request approval, approve, and reject flows with electronic
  signature support for approve decisions
- Add employee approvals page with dedicated tab and pending approvals view
- Add changelog field to publish and request approval flows
- Pre-select previous version's approvers in the publish dialog
- Show quorum approvers in document list with 100 approver hard limit
- Expose approval workflow through GraphQL, MCP, and CLI
- Remove legacy default approvers feature entirely
- Add comprehensive e2e test coverage for approval workflows

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

pkg/docgen/template.html

@@ -386,6 +386,7 @@
                                 <span class="classification">{{.Classification | classificationString}}</span>
                             </td>
                         </tr>
+                        {{- if gt (len .Approvers) 0}}
                         <tr>
                             <td>Approver{{- if gt (len .Approvers) 1}}s{{- end}}</td>
                             <td>
@@ -400,6 +401,7 @@
                                 {{- end}}
                             </td>
                         </tr>
+                        {{- end}}
                         <tr>
                             <td>Version:</td>
                             <td>{{.Version}}</td>