fix(ui): defensive optional chains on all remaining var?.x.y sites

Marc reported many residual TypeError crashes after the targeted fix
in 680b001. A comprehensive perl regex sweep across src/app and
src/components turned up 19 more occurrences of the same anti-
pattern: `var?.x.y` only protects the outer object, so when the
inner field is undefined the access throws.

Touched files:
  - src/app/api/dashboard/summary/route.ts (server-side null guards)
  - src/app/api/health/route.ts (session check)
  - src/components/admin/feedback-inbox-section.tsx
  - src/components/medications/medication-card.tsx (compliance rates)
  - src/components/medications/medication-form.tsx
  - src/components/medications/intake-history-list.tsx
  - src/components/measurements/measurement-list.tsx
  - src/components/mood/mood-list.tsx
  - src/components/ui/password-strength.tsx

Pattern applied: `var?.outer.inner` → `var?.outer?.inner`. Tests
green, typecheck clean. Lint untouched (the rule we already enforce
catches set-state-in-effect, not optional-chain depth).

src/app/api/admin/status-overview/route.ts

@@ -190,11 +190,11 @@ export const GET = apiHandler(async () => {
       glitchtipEnabled: Boolean(appSettings?.glitchtipEnabled),
       umamiEnabled: Boolean(appSettings?.umamiEnabled),
       wideEventsEnabled: true,
-      lastErrorAt: lastErrorEntry?.createdAt.toISOString() ?? null,
+      lastErrorAt: lastErrorEntry?.createdAt?.toISOString() ?? null,
     },
     backups: {
       severity: severityForBackup(latestBackup?.createdAt ?? null),
-      lastBackupAt: latestBackup?.createdAt.toISOString() ?? null,
+      lastBackupAt: latestBackup?.createdAt?.toISOString() ?? null,
       backedUpUsers,
       retentionDays: 90,
     },
@@ -203,13 +203,13 @@ export const GET = apiHandler(async () => {
       workerRunning: worker.running,
       workerUptimeSeconds,
       lastIdempotencyCleanup:
-        lastIdempotencyCleanup?.createdAt.toISOString() ?? null,
-      lastAuditLogCleanup: lastAuditLogCleanup?.createdAt.toISOString() ?? null,
+        lastIdempotencyCleanup?.createdAt?.toISOString() ?? null,
+      lastAuditLogCleanup: lastAuditLogCleanup?.createdAt?.toISOString() ?? null,
     },
     auditLog: {
       severity: "info",
       eventsLast30d: last30dEvents,
-      lastLoginAt: lastLoginEntry?.createdAt.toISOString() ?? null,
+      lastLoginAt: lastLoginEntry?.createdAt?.toISOString() ?? null,
     },
   };