fix(platform): address round 2 review findings

docs/tests/unit/vietnam-business-clock.md

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+# Test Evidence: Vietnam business-date clock boundary
+
+- **Test type:** Unit
+- **Requirement IDs:** `ACC-019`, `ACC-020`
+- **Scenario IDs:** `AC-ACC-010` (business-date boundary only)
+- **Test class/method:** `com.lab.labtimesheet.config.TimeConfigurationTest#utcInstantAtVietnamMidnightUsesTheNewLocalBusinessDate`
+- **Implementation commit:** `pending`
+
+## Protected behavior
+
+The production application clock uses `Asia/Ho_Chi_Minh`, so account lifecycle decisions based on `LocalDate.now`
+advance at Vietnam midnight rather than seven hours later at UTC midnight.
+
+## Test method
+
+The test obtains the real production clock configuration, fixes its configured zone at the UTC instant
+`2026-08-14T17:00:00Z`, and derives the local business date. No Spring context or database is needed because the
+contract under test is the clock bean's zone.
+
+## Hand-derived expected result
+
+Vietnam is UTC+07:00, so `2026-08-14T17:00:00Z` is `2026-08-15T00:00:00+07:00` and the business date is
+`2026-08-15`.
+
+## RED
+
+**Command**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+./mvnw -Dtest=TimeConfigurationTest test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
+Expected 2026-08-15 but was 2026-08-14 because the production clock used UTC.
+BUILD FAILURE
+```
+
+## GREEN
+
+**Command**
+
+```text
+./mvnw -Dtest=TimeConfigurationTest test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+```
+
+## Affected suite
+
+**Command and result**
+
+```text
+./mvnw -Dtest=TimeConfigurationTest,BootstrapIntegrationTest,SmtpOnboardingWebIntegrationTest,AccountActivationIntegrationTest,AccountWebIntegrationTest,BootstrapOnboardingWebIntegrationTest,JavaMailSmtpProbeTest,SecurityResponseIntegrationTest test
+Tests run: 22, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+PostgreSQL: 18.4
+```
+
+## External-test boundaries
+
+This verifies the production clock zone and its midnight boundary. It does not exercise later scheduler behavior or
+attendance-policy timezone versioning.