When a session has expired, require_role now bounces to /login?next=<path> and
sends the user back there after re-login.
- middleware: safe_next_url() (same-site relative path/query only; rejects
off-site, protocol-relative, javascript:, and the auth pages — no open
redirect). _login_redirect() builds the next param; for HTMX requests it uses
HX-Current-URL (the page, not the fragment) and HX-Redirect so the whole
browser navigates instead of swapping the login page into a fragment.
- login GET/POST carry `next` (hidden field), validated, used on success for
local + LDAP; OIDC stashes it in session across the IdP round-trip.
- login.html: hidden next field + next on the SSO link.
- tests for safe_next_url.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
