fix(chat): honor new-chat intent from secondary pages

Create a fresh local consultation for explicit new-chat navigation and keep reserved recovery from taking over its landing. Add regression tests and record validation gaps for remote review.

Co-Authored-By: Claude Code <noreply@anthropic.com>

frontend/src/app/(app)/page.tsx

@@ -1062,6 +1062,7 @@ export default function Home() {
         setStartGreeting(nextProfile.name.trim() ? createStartGreeting(nextProfile.name) : "");
         setOnboardingStep(missingProfileStep(nextProfile) ?? "name");
         setSessions(nextSessions);
+        if (bootstrapSelection.urlAction === "new-chat") writeSessionUrl(null, "replace");
         setActiveSessionId(landingSessionId);
         if (bootstrapSelection.clearStoredReturn) clearLoginSessionReturn();
         if (bootstrapSelection.urlAction === "replace-clear") writeSessionUrl(null, "replace");
@@ -1074,6 +1075,10 @@ export default function Home() {
         if (reservedConsultation?.status === "reserved") {
           const recoverySession = nextSessions.find((session) => session.id === reservedConsultation.sessionId);
           if (recoverySession) restoreConsultationRecovery(recoverySession, reservedConsultation.requestId, storedPending);
+          if (bootstrapSelection.urlAction === "new-chat") {
+            setActiveSessionId(landingSessionId);
+            setComposerNotice("");
+          }
         }
         if (modelCatalogResult.unavailable) {
           setComposerNotice("模型服务暂时不可用，当前无法发送问题。");