test: add frontend unit suite + fix mixed local/UTC timestamps

Two CODE_AUDIT items in one session.

§3.2 — Frontend regression net (js/tests/, 35 tests, node:test, zero deps):
- harness.js loads app.js (monofile, no exports) into a node:vm with browser
  globals stubbed, surfacing internals via an export epilogue.
- crypto: deriveKeyAndVerifier (AES key == raw PBKDF2, cross-checked vs Node
  pbkdf2Sync), legacy-vs-v2 verifier decoupling, encrypt/decrypt round-trip,
  IV uniqueness, AEAD tamper/wrong-key.
- csv: parseCSV tokenizer, findColumn heuristics, Bitwarden/KeePass mapping.
- merge: applyRemoteSnapshot add/update/skip (LWW), tombstone delete,
  resurrection arbitration (both NaN branches), local-tombstone veto,
  additive folder merge. Only api() is stubbed; loadEntries/encryptImportEntry
  run for real.
- Wired as a build gate in BuildAssets.ps1 (after node --check, bypass
  PM_SKIP_TESTS=1).

§2.2 — Unify timestamps on UTC:
- Entry created_at/updated_at were written via Delphi FormatDateTime(Now)
  = LOCAL, while deleted_at/tombstones use SQLite CURRENT_TIMESTAMP = UTC.
  The tombstone-resurrection arbitration compared the two zones, skewing by
  the machine's UTC offset even single-device.
- Add NowUTC/NowUTCStr to PM.Database, swap in at every entry/attachment
  write site (Entries create/update/bulk, Attachments POST echo).
- No JS change needed: arbitration now compares same-zone values.
- Existing rows self-heal on next edit (no destructive migration).

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

delphi-backend/Handlers/PM.Handler.Entries.pas

@@ -350,7 +350,7 @@ begin
     Exit;
   end;
 
-  LNow := FormatDateTime('yyyy-mm-dd hh:nn:ss', Now);
+  LNow := NowUTCStr;   // UTC — matches SQLite CURRENT_TIMESTAMP (see CODE_AUDIT §2.2)
 
   DB.Lock;
   try
@@ -493,7 +493,7 @@ begin
     Exit;
   end;
 
-  LNow := FormatDateTime('yyyy-mm-dd hh:nn:ss', Now);
+  LNow := NowUTCStr;   // UTC — matches SQLite CURRENT_TIMESTAMP (see CODE_AUDIT §2.2)
   DB.Lock;
   try
     LQ := TFDQuery.Create(nil);
@@ -1138,7 +1138,7 @@ begin
       Exit;
     end;
 
-    LNow := FormatDateTime('yyyy-mm-dd hh:nn:ss', Now);
+    LNow := NowUTCStr;   // UTC — matches SQLite CURRENT_TIMESTAMP (see CODE_AUDIT §2.2)
     LImported := 0;
     // Track newly-inserted IDs in input order so the client can upload
     // attachments to the right entry afterwards. Skipped rows emit -1