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/Source/PM.Database.pas

@@ -48,8 +48,29 @@ var
 procedure InitDatabase(const ADBPath: string);
 procedure DoneDatabase;
 
+// Current time as UTC. SQLite's CURRENT_TIMESTAMP / datetime('now') already
+// emit UTC, so every Delphi-written timestamp (created_at, updated_at,
+// deleted_at, …) MUST use these — mixing Delphi's local-time Now with the
+// SQLite-UTC values silently skews the sync last-write-wins / tombstone
+// resurrection arbitration by the machine's UTC offset (see CODE_AUDIT §2.2).
+function NowUTC: TDateTime;
+function NowUTCStr: string;   // 'yyyy-mm-dd hh:nn:ss' in UTC
+
 implementation
 
+uses
+  System.DateUtils;   // TTimeZone for local→UTC conversion
+
+function NowUTC: TDateTime;
+begin
+  Result := TTimeZone.Local.ToUniversalTime(Now);
+end;
+
+function NowUTCStr: string;
+begin
+  Result := FormatDateTime('yyyy-mm-dd hh:nn:ss', NowUTC);
+end;
+
 constructor TPMDatabase.Create(const ADBPath: string);
 begin
   inherited Create;