Closes#7. The issuer create/update handlers swallowed all service errors
as generic 500s. Now differentiates: 409 for UNIQUE constraint violations,
400 for unsupported issuer type, 404 for not-found on update, 500 for
unknown errors. Adds structured error logging via slog.
OnboardingWizard now pre-populates config field defaults when a type is
selected (matching IssuersPage behavior), preventing empty required fields
from causing silent failures.
install-agent.sh hardened for curl|bash usage: --agent-id flag, =value
syntax, /dev/tty stdin reopening, proper stderr routing in download_binary,
non-interactive install examples in help text, and updated wizard commands.
Adds adversarial security tests for EST, path traversal, and query
injection handlers.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>