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

templates/models/c4-event-based-integration/0200-containers/platform.archify

@@ -43,4 +43,4 @@ connections:
   - { from: router, to: store, label: append }
   - { from: router, to: notifier, label: notify }
   - { from: router, to: analytics, label: flatten }
-  - { from: router, to: dlq, label: failed, variant: dashed, labelDy: 24 }
+  - { from: router, to: dlq, label: failed, variant: dashed, labelDy: 24, decisions: [dead-letter-queue] }