refactor(js): extract TOTP module + add RFC 6238 tests (§3.1)

Fourth slice of the app.js split. Moves TOTP (base32Decode, generateTOTP,
parseOtpAuthUri) plus the TOTP-secret and custom-field AES-GCM wrappers to
js/app.totp.js. Loads before app.js (pure declarations), after app.crypto.js
(uses encryptPwd/decryptPwd). Also called by app.import.js and app.sync.js
via shared global scope.

- Byte-for-byte identical extraction; no duplicate const; syntax OK on all
  five app parts.
- NEW: js/tests/totp.test.js — 13 tests including the 5 RFC 6238 Appendix B
  reference vectors (generateTOTP reads Date.now(), so each case stubs the
  sandbox clock to the vector's fixed time), base32 decode edge cases, and
  parseOtpAuthUri. Extraction AND new coverage in one slice.
- Suite: 42 → 55 tests, all green.
- Assets regenerated (manifest now embeds all 6 ordered JS files:
  argon2 → crypto → totp → import → app → sync); also fixes the previous
  import commit's not-yet-rebuilt manifest.
- Delphi build artifacts (*.vrc, *.$manifest) gitignored.

app.js: 11936 → 10138 lines (4 modules extracted, ~1800 lines).

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

js/tests/totp.test.js

@@ -0,0 +1,94 @@
+// TOTP tests (js/app.totp.js) — cross-checked against the RFC 6238 Appendix B
+// reference vectors. generateTOTP reads Date.now() internally, so each case
+// stubs the sandbox clock to the vector's fixed time.
+//
+// RFC 6238 secret = ASCII "12345678901234567890" (20 bytes) → base32
+// "GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ". Appendix B lists 8-digit SHA-1 codes;
+// generateTOTP defaults to 6 digits, so the expectations are the last 6.
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { loadApp } = require('./harness.js');
+
+const ctx = loadApp();
+const T = ctx.__test;
+
+const RFC_SECRET = 'GEZDGNBVGY3TQOJQGEZDGNBVGY3TQOJQ';
+
+// Run generateTOTP as if the wall clock were `unixSec`. node --test isolates
+// each test file in its own process, so mutating the shared Date here can't
+// leak into other suites; we still restore to be tidy.
+async function codeAt(unixSec, period = 30, digits = 6) {
+    const orig = ctx.Date.now;
+    ctx.Date.now = () => unixSec * 1000;
+    try { return await T.generateTOTP(RFC_SECRET, period, digits); }
+    finally { ctx.Date.now = orig; }
+}
+
+test('base32Decode: RFC 6238 secret decodes to ASCII "12345678901234567890"', () => {
+    const bytes = T.base32Decode(RFC_SECRET);
+    assert.equal(new TextDecoder().decode(bytes), '12345678901234567890');
+});
+
+test('base32Decode: tolerates lowercase, spaces and padding', () => {
+    const a = T.base32Decode('JBSWY3DPEHPK3PXP');
+    const b = T.base32Decode('jbsw y3dp ehpk 3pxp==');
+    assert.equal(T.bytesToHex(a), T.bytesToHex(b));
+});
+
+test('base32Decode: throws on an invalid character', () => {
+    assert.throws(() => T.base32Decode('JBSW0189'), /Invalid base32/);  // 0/1/8/9 not in alphabet
+});
+
+// RFC 6238 Appendix B (SHA-1), 8-digit → last 6 digits for our 6-digit default.
+const VECTORS = [
+    [59,          '287082'],
+    [1111111109,  '081804'],
+    [1111111111,  '050471'],
+    [1234567890,  '005924'],
+    [2000000000,  '279037'],
+];
+
+for (const [t, expected] of VECTORS) {
+    test(`generateTOTP: RFC 6238 vector at t=${t} → ${expected}`, async () => {
+        const r = await codeAt(t);
+        assert.equal(r.code, expected);
+        assert.equal(r.period, 30);
+    });
+}
+
+test('generateTOTP: secondsLeft counts down within the 30s window', async () => {
+    // t=45 → 15s into the second window → 15 left.
+    const r = await codeAt(45);
+    assert.equal(r.secondsLeft, 15);
+    // t=59 → 29s into the window → 1 left.
+    assert.equal((await codeAt(59)).secondsLeft, 1);
+});
+
+test('generateTOTP: same window → same code (deterministic per period)', async () => {
+    const a = await codeAt(1234567890);
+    const b = await codeAt(1234567890 + 5);   // still the same 30s window
+    assert.equal(a.code, b.code);
+});
+
+test('parseOtpAuthUri: extracts the secret from an otpauth:// URI', () => {
+    assert.equal(
+        T.parseOtpAuthUri('otpauth://totp/Example:alice@example.com?secret=JBSWY3DPEHPK3PXP&issuer=Example'),
+        'JBSWY3DPEHPK3PXP');
+});
+
+test('parseOtpAuthUri: returns null for non-otpauth input', () => {
+    assert.equal(T.parseOtpAuthUri('https://example.com'), null);
+    assert.equal(T.parseOtpAuthUri('JBSWY3DPEHPK3PXP'), null);
+    assert.equal(T.parseOtpAuthUri(''), null);
+});
+
+test('parseOtpAuthUri → generateTOTP: parsed secret produces a valid 6-digit code', async () => {
+    const secret = T.parseOtpAuthUri('otpauth://totp/x?secret=' + RFC_SECRET);
+    const orig = ctx.Date.now;
+    ctx.Date.now = () => 59 * 1000;
+    try {
+        const r = await T.generateTOTP(secret, 30, 6);
+        assert.equal(r.code, '287082');
+    } finally { ctx.Date.now = orig; }
+});