test(sweep): add UI-sweep targets for the new syncing / no-peers / chat-identity states

Capture the states the earlier verification couldn't reach:
- overview-syncing: the balance "catching up — funds are safe" strip (P4).
- overview-no-peers: the node-status banner's no-peers detail (P2; full-node
  only — renders as a plain Overview in the Lite sweep binary).
- chat-identity-preparing / -unavailable: the chat empty states that used to
  all say "unlock your wallet" (P3). Setup clears the fabricated demo identity
  (clearIdentity wipes only the key; the demo message store survives);
  sweepEnsureDemoChatIdentity() re-fabricates on teardown so later targets keep
  the populated chat UI.

Also make the demo baseline a genuinely synced node (tip_known=true) so the
no-peers banner only appears on its own target, and dismiss the lite first-run
welcome prompt during the demo so it stops occluding every lite screenshot
(snapshotted + restored). Verified: all four new captures render correctly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app.h

@@ -1677,6 +1677,7 @@ private:
     std::string sweep_sandbox_;
     bool sweep_chat_identity_fabricated_ = false;   // seedChatDemoData() made the demo chat identity
     void applyHealthyDemoState();  // reset the connection/encryption flags to the healthy demo values
+    void sweepEnsureDemoChatIdentity();  // re-fabricate a demo chat identity if none (sweep teardown)
     void writeSweepManifest() const;
     // Snapshot of the state_ fields the demo installer mutates, restored at sweep end. Kept as a
     // plain struct because WalletState has reference-alias members and isn't copy-assignable.
@@ -1692,6 +1693,7 @@ private:
         double market_price_usd=0;
         double market_change_24h=0;
         WizardPhase wizard_phase = WizardPhase::None;   // the demo state dismisses the wizard
+        bool lite_firstrun_dismissed = false;           // the demo dismisses the lite welcome prompt
     } sweep_state_snapshot_;
     bool  sidebar_user_toggled_ = false; // user manually toggled — suppress auto-collapse
     float sidebar_width_anim_ = 0.0f;  // animated width (0 = uninitialized)