FEST offline lookup: dataset contract, cached repository, ranked search

Milestone 8. docs/fest-dataset.md is the interface to the out-of-repo
server job that flattens the M30 Rekvirent extract (FEST, not
Felleskatalogen — decision #8) into slim JSON. The repository
downloads on demand, parses BEFORE overwriting the cache (a failed
refresh can never clobber a working dataset), and serves all searches
from memory. Ranking (prefix > word-prefix > substring) is a pure
object with tests. Every failure mode degrades to manual entry —
autocomplete is a convenience, never a gate.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/fest-dataset.md

@@ -0,0 +1,51 @@
+# FEST slim dataset — contract
+
+The app does **offline** autocomplete against a slim, pre-flattened JSON file.
+The job that produces it lives **outside this repo**: it pulls FEST's open
+Rekvirent extract (the M30 SOAP/WCF XML dump from DMP), flattens the
+human-use medication entries, and publishes the JSON behind Caddy or into the
+Garage bucket. FEST changes slowly; refresh the published file monthly-ish.
+
+Why FEST and not Felleskatalogen: FEST is the open national dataset;
+Felleskatalogen is licensed editorial content with no open API. Why not live
+lookups: M30 is a bulk XML dump, not a per-keystroke API — and the phone must
+work offline.
+
+## Where the app loads it from
+
+`Innstillinger → FEST-URL` (e.g. `https://<host>/fest/slim.json`). The app
+downloads on demand, caches to `filesDir/fest-slim.json`, and reads only the
+cache afterwards. A staleness nudge appears after ~45 days (dataset `updated`
+field), but old data keeps working — autocomplete is a convenience, never a
+gate.
+
+## JSON shape (version 1)
+
+```json
+{
+  "version": 1,
+  "updated": "2026-06-01",
+  "entries": [
+    {
+      "name": "Paracet",
+      "strength": "500 mg",
+      "unit": "tablett",
+      "form": "tablett",
+      "atc": "N02BE01",
+      "packageSize": 20.0
+    }
+  ]
+}
+```
+
+- `name` — preparation name (varenavn), required.
+- `strength` — display string, may be empty.
+- `unit` — what one dose counts ("tablett", "ml", "dose"), required.
+- `form` — FEST's form text, free-form (not this app's MedForm enum; the
+  editor maps it heuristically and lets the user override).
+- `atc` — ATC code, optional.
+- `packageSize` — units per package for the most common package, optional.
+
+Unknown extra keys are ignored (`ignoreUnknownKeys`), so the producer can add
+fields without breaking older app versions. Bump `version` only for breaking
+changes.