refactor(js): extract import/export module from app.js monofile (§3.1)

Third slice of the app.js split. Moves the encrypted export container,
CSV/JSON import parsing (parseCSV, findColumn, parseEntriesFromCSV,
parseEntriesFromJSON), and the doImport/doExport/doExportCSV flows to
js/app.import.js. encryptImportEntry moves here too (also called by
app.sync.js — resolved via shared global scope at call time).

- Byte-for-byte identical to the extracted block; no duplicate const;
  no top-level import ref left in app.js.
- Load order: BEFORE app.js (pure declarations, no top-level side effects),
  alongside app.crypto.js. Full order: argon2 → crypto → import → app → sync.
- index.html + BuildAssets whitelist + harness APP_PARTS updated.
- Safety net: the 14 CSV tests exercise parseCSV/parseEntriesFromCSV from
  the extracted file and stay green (42/42).

app.js: 11936 → 10253 lines (crypto + sync + import now separate, ~1700
lines moved into 3 modules).

NOTE: assets.res not regenerated here (needs brcc32/Delphi) — run
BuildAssets before the next Delphi build to embed js/app.import.js.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CODE_AUDIT.md

@@ -228,8 +228,12 @@ réécriture des call-sites, risque quasi nul vs conversion en modules ES).
   identique, 42 tests verts, pas de `const` dupliqué. Chargé AVANT app.js.
 - ✅ `js/app.sync.js` extrait (WebDAV, snapshot, merge `applyRemoteSnapshot`)
   — byte-for-byte identique, couvert par les tests merge, chargé APRÈS app.js
-  (effet de bord top-level `Bridge.onWebdavResult`). Pattern + règles d'ordre
+  (effet de bord top-level `Bridge.onWebdavResult`).
+- ✅ `js/app.import.js` extrait (export container + parsing CSV/JSON +
+  `doImport`/`doExport`) — byte-for-byte identique, couvert par les 14 tests
+  CSV, chargé AVANT app.js (pures déclarations). Pattern + règles d'ordre
   documentés dans CLAUDE.md « Découpage frontend ».
+- `app.js` : 11 936 → **10 253 lignes** (crypto + sync + import sortis).
 - Reste à extraire (grosses sections cohésives) : slideover, settings,
   quicksearch, autofill, auto-backup…
 - ✅ `node --check` en pré-étape de `BuildAssets.ps1` : **déjà fait** (cf. §3.2).