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

test/fixtures/model/0200-containers/online-shop.archify

@@ -3,6 +3,7 @@ diagram_type: architecture
 meta:
   title: Containers
   output: containers.html
+decisions: [postgres-as-source-of-truth]
 components:
   - ref: customer
     pos: [40, 160]
@@ -22,6 +23,7 @@ components:
   - ref: queue
     pos: [460, 360]
     size: [130, 60]
+    decisions: [queue-between-api-and-worker]
   - ref: worker
     pos: [670, 460]
     size: [130, 60]
@@ -34,6 +36,6 @@ connections:
   - { from: web, to: api, label: JSON }
   - { from: api, to: cache, label: read }
   - { from: api, to: db, label: SQL }
-  - { from: api, to: queue, label: enqueue, labelAt: [560, 290] }
+  - { from: api, to: queue, label: enqueue, labelAt: [560, 290], decisions: [queue-between-api-and-worker] }
   - { from: queue, to: worker, label: poll }
   - { from: worker, to: db, label: SQL, labelAt: [735, 420] }

test/fixtures/model/decisions/0001-postgres-as-source-of-truth.archify-decision

@@ -0,0 +1,20 @@
+schema_version: 1
+decision:
+  id: postgres-as-source-of-truth
+  title: PostgreSQL as the single source of truth
+  status: accepted
+  date: 2026-09-02
+  elements: [db, api, worker]
+  diagrams: [0200-containers/online-shop.archify]
+context: >
+  Orders, customers and the catalogue were spread over the
+  shop database and two spreadsheets kept by support.
+  Refunds were reconciled by hand every Monday.
+decision: >
+  One PostgreSQL database owns orders, customers and the
+  catalogue. The API is the only writer. Everything else
+  (cache, search, reports) is derived and may be rebuilt.
+consequences: >
+  Support loses the spreadsheets and gets the admin console.
+  Any new store must be declared derived or get its own
+  decision. Backups and migrations are the API team's job.

test/fixtures/model/decisions/0002-queue-between-api-and-worker.archify-decision

@@ -0,0 +1,20 @@
+schema_version: 1
+decision:
+  id: queue-between-api-and-worker
+  title: A queue between the API and the worker
+  status: accepted
+  date: 2026-09-16
+  elements: [api, queue, worker]
+  diagrams: [0200-containers/online-shop.archify]
+context: >
+  Order confirmation emails and invoices were sent inside
+  the checkout request. A slow mail provider made checkout
+  slow; a failing one made checkout fail.
+decision: >
+  The API enqueues a job per side effect on SQS. One worker
+  service consumes the queue and does the slow work.
+  Checkout returns as soon as the order is stored.
+consequences: >
+  Emails arrive seconds later, not instantly. Jobs must be
+  idempotent because SQS delivers at least once. The worker
+  is the second place that writes to the database.

test/fixtures/model/decisions/0003-opensearch-for-product-search.archify-decision

@@ -0,0 +1,20 @@
+schema_version: 1
+decision:
+  id: opensearch-for-product-search
+  title: OpenSearch for product search
+  status: proposed
+  date: 2026-10-19
+  elements: [api, worker, db]
+  diagrams: [0200-containers/online-shop.archify]
+context: >
+  Catalogue search runs as SQL LIKE queries on the
+  database. Typos find nothing and the catalogue page is
+  the slowest page in the shop.
+decision: >
+  Add a dedicated search service on OpenSearch. The API
+  queries it; the worker rebuilds the index from the
+  database after every catalogue change.
+consequences: >
+  The index is derived data under decision 0001 and may be
+  rebuilt at any time. One more service to run. Search
+  results can lag the database by the rebuild interval.