feat(ui): large-wallet nudge as a one-time toast + clickable alert

Extend the wallet-bloat warning beyond the Settings banner: when wallet.dat
first crosses 500 MB (full-node, synced), fire a one-time warning toast plus a
clickable "Consolidate notes…" entry in the bell/alerts panel that opens Merge
to Address. The persisted large_wallet_warned flag keeps it once-only and
re-arms if the file later shrinks back under the threshold.

- AlertRecord gains an optional onClick + actionHint; Notifications::action()
  pushes a toast and a clickable history entry. renderAlertHistoryPanel() now
  renders the accent action link (under the message) and measures true content
  height so wrapped messages + the link aren't clipped.
- App::maybeWarnLargeWallet() (mirrors maybeRemindSeedBackup) runs once per
  launch from update(); reuses the existing wallet_size_warn/consolidate strings.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/app.h

@@ -817,6 +817,7 @@ private:
     // install) to back up their seed phrase. Cheap early-outs keep it idle until it can act.
     void maybeRemindSeedBackup();
     void maybeWarnEmptyWalletWithFundedSiblings();  // full-node: empty active wallet + a funded sibling → warn once
+    void maybeWarnLargeWallet();                    // full-node: wallet.dat past bloat threshold → one-time toast + clickable alert
     void scanFundedSiblingsAsync();                 // off-UI-thread probe of sibling wallet files
     static void scrubAndRemoveExport(const std::string& path);  // zero + delete a plaintext key export (H-02)
     void sweepStaleDecryptExports();                // startup net: purge stale obsidiandecryptexport* files (H-02)
@@ -1007,6 +1008,7 @@ private:
     bool seed_backup_loading_ = false;
     bool seed_backup_no_mnemonic_ = false;
     bool seed_backup_reminder_in_flight_ = false;  // guards the one-time backup nudge probe
+    bool large_wallet_checked_ = false;            // gate: stat wallet.dat for the bloat nudge once per launch
 
     // Cached mnemonic status of the current wallet, driving the Migrate-to-seed button glow. Probed
     // once per connect (probeWalletSeedStatus, via exportSeedPhrase); NoMnemonic = a legacy wallet a