fix(security): apply audit remediations to dev (ported + dev-only)

Dev-branch audit (docs/_archive/security-audit-dev-2026-07-22.md) re-found the
master issues (absent on dev) plus new ones in dev-only code. Applied here;
full-node build + test suite green; the subtle fixes were adversarially re-verified.

Ported from the master remediation (adapted to dev's code):
- bootstrap: reject zip-slip / path-traversal archive members (isSafeArchivePath)
  before writing (S2-1). (dev already fail-closes on a missing checksum.)
- xmrig updater: fail closed when a signature is required but no key is pinned (F1-1).
- http_download.httpGetString: 16 MiB hard cap + MAXFILESIZE on the shared
  metadata/price fetch (F1-2 / caps the updater + exchange paths at one site).
- rpc_client: explicit SSL_VERIFYPEER/VERIFYHOST (F4-1) and a 256 MiB response
  cap in WriteCallback (F4-3).
- lite_connection_service: reject remote http:// lite servers, loopback only (L1-1).
  Loopback is matched by a strict dotted-decimal 127.0.0.0/8 check (not a
  startsWith("127.") prefix, which would wrongly accept 127.0.0.1.evil.com), with
  userinfo/fragment stripping.
- lite controller: propagate encrypt/decrypt save() failure instead of reporting
  success (F7-1).
- xmrig_manager: chmod(0600) the pool config before writing secrets (F5-2).
- app: clear the copied secret from the OS clipboard on shutdown (F3b-1).
- export_transactions: neutralize CSV/spreadsheet formula injection (F13-1).
- build pipeline: build-from-source lite backend + remove the self-attested
  CMake signature gate (F15-1); pinned+verified appimagetool (F15-3/4);
  verified Sapling params in setup.sh (F15-6); build.sh exits 0 on success.
  (F14-1 empty-quoted-arg and F8-2 NUL-termination were already fixed on dev.)

Dev-only findings:
- rpc_client.callRaw: scrub the raw buffer + parsed tree (templated scrubJsonSecrets
  for ordered_json) so console dumpprivkey/z_exportkey keys don't linger in freed
  heap (N1-1).
- seed_wallet_creator: wipe the exported mnemonic on the failure path so a discarded
  failed result never carries a live seed (W1-2).
- export_all_keys: write the plaintext key dump 0600 + atomically via
  writeFileAtomically (U1-2).
- chat_database: restrict chat_messages.sqlite and its WAL/SHM sidecars to owner-only (C3-1).

Not done (need a decision, documented in the report):
- Chat header metadata (cid/z/p) rides outside the AEAD (C1/C2) — binding it is a
  wire-protocol change requiring SilentDragonXLite interop review.
- Bootstrap lacks an offline-rooted signature (S2-2 residual) — needs signing infra.
- Console scrollback retains console-typed key-export output in plaintext (N1-1
  residual) — inherent to an echoing console; would need output redaction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app.cpp

@@ -5320,6 +5320,11 @@ void App::renderLoadingOverlay(float contentH)
 
 void App::shutdown()
 {
+    // Wipe any copied secret from the OS clipboard before we exit — the 45s auto-clear timer
+    // never fires if the user quits sooner, which would otherwise leave a key/seed resident.
+    // (ImGui context is still alive here; App::shutdown() runs before ImGui::DestroyContext().)
+    clearSecretClipboardIfArmed();
+
     // Clean up bootstrap if running
     if (bootstrap_) {
         bootstrap_->cancel();
@@ -5522,10 +5527,9 @@ void App::copySecretToClipboard(const std::string& secret)
         ui::Notifications::instance().info("Copied — clipboard auto-clears in 45s", 4.0f);
 }
 
-void App::pumpSecretClipboardClear()
+void App::clearSecretClipboardIfArmed()
 {
-    if (clipboard_clear_deadline_ <= 0.0) return;
-    if (ImGui::GetTime() < clipboard_clear_deadline_) return;
+    if (clipboard_secret_hash_ == 0) return;
     // Only clear if the clipboard STILL holds our secret (the user may have copied something else).
     if (const char* cb = ImGui::GetClipboardText()) {
         std::uint64_t h = 1469598103934665603ULL;
@@ -5536,6 +5540,13 @@ void App::pumpSecretClipboardClear()
     clipboard_secret_hash_ = 0;
 }
 
+void App::pumpSecretClipboardClear()
+{
+    if (clipboard_clear_deadline_ <= 0.0) return;
+    if (ImGui::GetTime() < clipboard_clear_deadline_) return;
+    clearSecretClipboardIfArmed();
+}
+
 void App::maybeFinishTransactionSendProgress()
 {
     using Job = services::NetworkRefreshService::Job;