fix(platform): address round 2 review findings

docs/tests/web/account-uniqueness-feedback.md

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+# Test Evidence: Constraint-specific account uniqueness feedback
+
+- **Test type:** Web
+- **Requirement IDs:** `ACC-019`, `DB-003`
+- **Scenario IDs:** `AC-ACC-005` (Intern creation uniqueness boundary)
+- **Test class/method:** `com.lab.labtimesheet.feature.account.controller.AccountWebIntegrationTest#duplicateNormalizedStudentCodeIsReportedOnStudentCodeRatherThanEmail`
+- **Implementation commit:** `pending`
+
+## Protected behavior
+
+A case- and whitespace-normalized duplicate Intern student code is reported on the student-code field. A distinct
+email is not falsely labeled as duplicate, and unknown uniqueness constraints fall back to a non-specific conflict.
+
+## Test method
+
+MockMvc creates one Intern through the authenticated CSRF-protected production form and then submits a second Intern
+with a distinct email and the same student code in different case with surrounding whitespace. PostgreSQL 18.4
+enforces the real Flyway expression index; the controller maps Hibernate's known constraint name to the form field.
+
+## Hand-derived expected result
+
+The second request returns HTTP 200 on `accounts/new`, retains the safe display name, shows the student-code conflict,
+and does not claim that the distinct email already exists.
+
+## RED
+
+**Command**
+
+```text
+export JAVA_HOME=/opt/homebrew/opt/openjdk@25
+export PATH="$JAVA_HOME/bin:$PATH"
+export DOCKER_HOST=unix:///Users/sechmachine/.orbstack/run/docker.sock
+./mvnw -Dtest=AccountWebIntegrationTest#duplicateNormalizedStudentCodeIsReportedOnStudentCodeRatherThanEmail test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 1, Errors: 0, Skipped: 0
+PostgreSQL reported uq_intern_profiles_student_code_ci, but the form displayed "this email already exists".
+BUILD FAILURE
+PostgreSQL: 18.4
+```
+
+## GREEN
+
+**Command**
+
+```text
+./mvnw -Dtest=AccountWebIntegrationTest#duplicateNormalizedStudentCodeIsReportedOnStudentCodeRatherThanEmail test
+```
+
+**Observed result**
+
+```text
+Tests run: 1, Failures: 0, Errors: 0, Skipped: 0
+BUILD SUCCESS
+PostgreSQL: 18.4
+```
+
+## 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
+
+The test covers the two Platform-owned normalized identity constraints. It does not enumerate later-iteration feature
+constraints or perform a real-browser accessibility pass.