feat(import): carry every field the app's own files write

The JSON import read six measurement fields and six mood fields while
the full backup and the JSON export carry twice that. A sleep night came
back as stageless rows, a range reading as a single value, an ECG alert
without its verdict, and a mood entry without its note, its level-A
values, its zone, its tag and factor links or its day context.

The import now reads valueMin/valueMax, sleepStage,
rhythmClassification and deviceType on a reading, and note, a1 to a5,
tz, factors, structuredTags and context on a mood entry. Each mood entry
is written with its links and context in one transaction, the way the
bulk mood ingest writes one. A link to a tag the importing account does
not have is dropped and named in droppedTagKeys / droppedFactorKeys, and
the import card says which. The schema moves to
src/lib/import/json/schema.ts so the guards can read it.

json-import-field-coverage.test.ts runs the JSON export and both backup
variants on an account with every column filled in: every field they
write is either read by the import or named with the reason it is not
(row ids, source, deletion records, ciphertext, sync bookkeeping), and a
reason for a field no exporter writes fails as stale. The round trip
imports each file into a fresh account and compares the re-export field
for field. The published contract is held to the runtime schema.

src/__tests__/baselines/source-function-lines.json

@@ -1,7 +1,7 @@
 {
   "$comment": "Production functions over 200 lines, keyed \"file :: name\", and their length. Maintained by src/__tests__/source-size-ratchet.test.ts.",
-  "count": 355,
-  "total": 114640,
+  "count": 354,
+  "total": 114417,
   "entries": {
     "app/achievements/page.tsx :: AchievementsPage": 206,
     "app/api/admin/backups/upload/route.ts :: apiHandler(arg)": 314,
@@ -208,7 +208,6 @@
     "components/settings/import-panel/csv-import-card.tsx :: CsvImportCard": 212,
     "components/settings/import-panel/dose-history-import-card.tsx :: DoseHistoryImportCard": 225,
     "components/settings/import-panel/health-connect-import-card.tsx :: HealthConnectImportCard": 293,
-    "components/settings/import-panel/json-import-card.tsx :: JsonImportCard": 223,
     "components/settings/import-panel/record-csv-import-card.tsx :: RecordCsvImportSheet": 460,
     "components/settings/insights-pill-order-section.tsx :: InsightsPillOrderSection": 255,
     "components/settings/integrations/connections-panel.tsx :: ConnectionsPanel": 230,