feat(settings): drawing_properties_get/set — SummaryInfo on COM, custom properties on both engines

Summary fields are refused headlessly with capability dwgprops before any
write; custom properties are $CUSTOMPROPERTYTAG/$CUSTOMPROPERTY pairs and
survive save + reopen. Validation is shared, by name, and never str()-coerces.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

docs/tool-inventory.json

@@ -3,7 +3,7 @@
   "schema_version": 1,
   "package_version": "1.5.1",
   "totals": {
-    "tools": 167,
+    "tools": 169,
     "resources": 8,
     "prompts": 5,
     "groups": 20
@@ -14,7 +14,7 @@
     "blocks": 9,
     "corner_ops": 4,
     "dimensions": 5,
-    "drawing": 11,
+    "drawing": 13,
     "engineering": 10,
     "entity_creation": 18,
     "entity_modification": 16,
@@ -631,6 +631,34 @@
         "readOnlyHint": true
       }
     },
+    {
+      "name": "drawing_properties_get",
+      "group": "drawing",
+      "cost": "read",
+      "summary": "Read the drawing's title, subject, author, keywords, comments and custom properties.",
+      "tags": [
+        "drawing",
+        "settings"
+      ],
+      "annotations": {
+        "title": "Drawing Properties (read)",
+        "readOnlyHint": true
+      }
+    },
+    {
+      "name": "drawing_properties_set",
+      "group": "drawing",
+      "cost": "safe",
+      "summary": "Set the drawing's summary fields and add, change or delete custom properties.",
+      "tags": [
+        "drawing",
+        "settings"
+      ],
+      "annotations": {
+        "title": "Drawing Properties (write)",
+        "readOnlyHint": false
+      }
+    },
     {
       "name": "drawing_purge",
       "group": "drawing",