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>

CLAUDE.md

@@ -33,11 +33,16 @@ visibles des suivants exactement comme dans le monofichier. Ordre actuel :
 ```
 js/argon2.js      (IIFE, globalThis.NobleArgon2)
 js/app.crypto.js  (KDF, verifier, encrypt/decrypt — extrait §3.1)
+js/app.import.js  (export container + import CSV/JSON — extrait §3.1)
 js/app.js         (le reste : state, Bridge, api, UI…)
 js/app.sync.js    (WebDAV + merge — extrait §3.1, APRÈS app.js car
                    effet de bord top-level `Bridge.onWebdavResult = …`)
 ```
 
+`app.import.js` contient `encryptImportEntry`, appelé aussi par
+`app.sync.js` (`applyRemoteSnapshot`) — OK, référence cross-fichier résolue
+au call-time via le scope global partagé.
+
 Note ordre : un module **sans** exécution top-level (que des déclarations,
 comme `app.crypto.js`) peut se charger AVANT `app.js`. Un module **avec** un
 effet de bord top-level qui touche un global d'`app.js` (`Bridge`, `state`…)
@@ -94,6 +99,7 @@ parsing CSV d'import, et l'arbitrage merge/tombstone de sync
 | Handlers REST | `delphi-backend/Handlers/PM.Handler.*.pas` |
 | Frontend principal (en cours de découpage §3.1) | `js/app.js` |
 | Crypto frontend (KDF, verifier, AES-GCM) — extrait §3.1 | `js/app.crypto.js` |
+| Import/export frontend (CSV/JSON parse, export container) — extrait §3.1 | `js/app.import.js` |
 | Sync frontend (WebDAV, snapshot, merge) — extrait §3.1 | `js/app.sync.js` |
 | Argon2id vendé (bundle `@noble/hashes`, IIFE) | `js/argon2.js` |
 | HTML racine | `index.html` |