Redesign document approval flow

Replace the per-approver add/remove model with a quorum-based approval
system. Documents now have default approvers that are pre-populated when
requesting approval, and the publish dialog lets users adjust the list
before submitting.

Key changes:

- Add PENDING_APPROVAL document version status with dedicated transitions
- Introduce approval quorums with request/approve/reject/void lifecycle
- Add default approvers per document (stored in document_default_approvers)
  with MERGE-based upsert for efficient sync
- Add NoDuplicates validator for slice fields
- Split ALTER TYPE ADD VALUE migrations into separate files (required by
  PostgreSQL when run inside transactions)
- Use VOIDED consistently for both quorum status and decision state enums
- Expose void/approve/reject through GraphQL and MCP, with e2e tests
- Add approval management UI: publish dialog with approver selection,
  approval list with void support, and external approve/reject page

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

pkg/validator/validator_common_test.go

@@ -264,3 +264,65 @@ func TestRequired(t *testing.T) {
 		}
 	})
 }
+
+func TestNoDuplicates(t *testing.T) {
+	t.Run("nil slice", func(t *testing.T) {
+		var slice []string
+		err := NoDuplicates()(slice)
+		if err != nil {
+			t.Errorf("expected no error for nil slice, got: %v", err)
+		}
+	})
+
+	t.Run("empty slice", func(t *testing.T) {
+		slice := []string{}
+		err := NoDuplicates()(slice)
+		if err != nil {
+			t.Errorf("expected no error for empty slice, got: %v", err)
+		}
+	})
+
+	t.Run("unique strings", func(t *testing.T) {
+		slice := []string{"a", "b", "c"}
+		err := NoDuplicates()(slice)
+		if err != nil {
+			t.Errorf("expected no error, got: %v", err)
+		}
+	})
+
+	t.Run("duplicate strings", func(t *testing.T) {
+		slice := []string{"a", "b", "a"}
+		err := NoDuplicates()(slice)
+		if err == nil {
+			t.Fatal("expected validation error for duplicates")
+		} else if err.Code != ErrorCodeInvalidFormat {
+			t.Errorf("expected error code %s, got %s", ErrorCodeInvalidFormat, err.Code)
+		}
+	})
+
+	t.Run("unique ints", func(t *testing.T) {
+		slice := []int{1, 2, 3}
+		err := NoDuplicates()(slice)
+		if err != nil {
+			t.Errorf("expected no error, got: %v", err)
+		}
+	})
+
+	t.Run("duplicate ints", func(t *testing.T) {
+		slice := []int{1, 2, 1}
+		err := NoDuplicates()(slice)
+		if err == nil {
+			t.Fatal("expected validation error for duplicates")
+		}
+	})
+
+	t.Run("non-comparable elements", func(t *testing.T) {
+		slice := []map[string]string{{"a": "b"}}
+		err := NoDuplicates()(slice)
+		if err == nil {
+			t.Fatal("expected validation error for non-comparable elements")
+		} else if err.Code != ErrorCodeInvalidFormat {
+			t.Errorf("expected error code %s, got %s", ErrorCodeInvalidFormat, err.Code)
+		}
+	})
+}