feat(security): cookie session idle-timeout + LDAP-free role-mapping refresh (#15, M2.19)

Spike outcome: the shared ILdapAuthService (ZB.MOM.WW.Auth.Abstractions, an external
NuGet package) exposes ONLY AuthenticateAsync(username, password, ct) — no passwordless
service-account group-search. A live LDAP group re-query for an active session therefore
requires a new lib method and is OUT OF SCOPE (cannot modify the external package).
Implemented the always-achievable layers (cookie-only; no embedded JWT for cookie principals):

- /auth/login now stores the user's raw LDAP groups (one zb:group claim each) plus a
  zb:lastrolerefresh anchor (login time, UTC), seeding the LastActivity idle anchor too.
- SessionClaimBuilder: single shared DRY claim-builder used by BOTH /auth/login AND the
  refresh path, so the two claim shapes cannot drift (canonical identity/role/scope claims
  with nameType/roleType pinned, plus the M2.19 group + refresh-anchor additions).
- CookieSessionValidator (TimeProvider-injected, unit-testable) + a thin
  CookieAuthenticationEvents.OnValidatePrincipal adapter:
    * idle-timeout: a session past IdleTimeoutMinutes (default 30) is RejectPrincipal+SignOut;
      consistent with the cookie ExpireTimeSpan+SlidingExpiration window (same value).
    * role refresh WITHOUT LDAP: when older than RoleRefreshThresholdMinutes (new option,
      default 15) the DB-backed RoleMapper re-runs on the STORED groups, claims are rebuilt
      via the shared builder, the anchor advances, principal is replaced + cookie renewed.
      Revoked DB mappings drop the user's roles mid-session.
    * fail-soft: any refresh error KEEPS the existing principal (no sign-out, never throws)
      — mirrors the documented "LDAP failure: active sessions continue with current roles".
- Documented residual limitation in Component-Security.md: central role-mapping/scope
  changes apply within ~15 min without LDAP; live directory group-membership changes are
  picked up only at next login (needs a passwordless group-search on the external
  ZB.MOM.WW.Auth.Ldap lib — tracked follow-up).

Tests (Security.Tests, all green): CookieSessionValidatorTests + SessionClaimBuilderParityTests
— idle reject/keep, LDAP-free remap-from-stored-groups, revoked-roles loss, sub-threshold
no-refresh, refresh-throws-keeps-session, and login/refresh claim-parity.

docs/plans/2026-06-15-stillpending-m2-implementation.md.tasks.json

@@ -19,8 +19,8 @@
     {"id": 47, "ref": "M2.15", "subject": "M2.15 #29: register site active-node purge gate (DI)", "class": "small", "status": "completed", "commits": ["e1ee37e"]},
     {"id": 48, "ref": "M2.16", "subject": "M2.16 #30: Health Monitoring consumes FailedWriteCount", "class": "small", "status": "completed", "commits": ["d81f747", "c9244d8"]},
     {"id": 49, "ref": "M2.17", "subject": "M2.17 #31: reconcile StateTransitionValidator delete-from-NotDeployed", "class": "small", "status": "completed", "commits": ["c104356"]},
-    {"id": 50, "ref": "M2.18", "subject": "M2.18 #26: debug-stream stream-first ordering + replay/dedup", "class": "high-risk", "status": "completed", "commits": ["d8519cb"]},
-    {"id": 51, "ref": "M2.19", "subject": "M2.19 #15: LDAP periodic re-query for interactive sessions (spike+impl)", "class": "high-risk", "status": "pending"}
+    {"id": 50, "ref": "M2.18", "subject": "M2.18 #26: debug-stream stream-first ordering + replay/dedup", "class": "high-risk", "status": "completed", "commits": ["d8519cb", "a0d9379"]},
+    {"id": 51, "ref": "M2.19", "subject": "M2.19 #15: LDAP periodic re-query for interactive sessions (spike+impl)", "class": "high-risk", "status": "completed", "note": "Spike outcome: shared ILdapAuthService exposes only AuthenticateAsync (no passwordless group-search) -> live LDAP group re-query out of scope (external pkg, tracked follow-up). Implemented always-achievable layers: stored zb:group + zb:lastrolerefresh claims at login, shared SessionClaimBuilder (DRY login+refresh), CookieSessionValidator + OnValidatePrincipal (idle-timeout reject@30m, DB-only role-mapping refresh@15m, fail-soft keep-session on refresh error). Residual limitation documented in Component-Security.md.", "commits": ["9cfa660"]}
   ],
   "deferred": [
     {"ref": "#16", "subject": "Transport stale-instance enumeration", "to": "M8 (Transport)"},