Architecture decisions: files, diagram references, views and panels

- *.archify-decision files: id (unique, words), title, status, date,
  elements, diagrams, supersedes, and prose; parsed, merged and link-checked
  in the model index; diagnostics on the file
- diagrams point at decisions with decisions: [...] on the diagram, nodes
  and edges; stripped before Archify, unknown ids reported, completion,
  hover and go-to-definition for the ids and for elements/diagrams/
  supersedes in decision files
- Decisions panel on the main.archify page; Decisions rail panel under a
  diagram (hover lights up the node or connection); decisions on element
  cards and in the element dialog; decision view for the file, with a
  lost-model note outside a model
- Archify | New Decision… command and template; editor schemas; the three
  New Model examples carry decisions; docs, changelog, 0.8.0

schemas/architecture.schema.json

@@ -219,6 +219,14 @@
           "diagram": {
             "type": "string",
             "description": "Diagram that explains this element, relative to the model root (main.archify). Double-click the node to open it."
+          },
+          "decisions": {
+            "type": "array",
+            "items": {
+              "type": "string",
+              "minLength": 1
+            },
+            "description": "Ids of architecture decisions (*.archify-decision files of the model) this is about. Shown in the Decisions panel under the diagram."
           }
         },
         "anyOf": [
@@ -332,6 +340,14 @@
           },
           "width": {
             "$ref": "common.schema.json#/$defs/relationshipWidth"
+          },
+          "decisions": {
+            "type": "array",
+            "items": {
+              "type": "string",
+              "minLength": 1
+            },
+            "description": "Ids of architecture decisions (*.archify-decision files of the model) this is about. Shown in the Decisions panel under the diagram."
           }
         }
       }
@@ -363,6 +379,14 @@
           "description": "What the model covers; shown on the model page."
         }
       }
+    },
+    "decisions": {
+      "type": "array",
+      "items": {
+        "type": "string",
+        "minLength": 1
+      },
+      "description": "Ids of architecture decisions (*.archify-decision files of the model) this is about. Shown in the Decisions panel under the diagram."
     }
   }
 }