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>

scripts/create-appimage.sh

@@ -24,18 +24,27 @@ if [ ! -f "${BUILD_DIR}/bin/ObsidianDragon" ]; then
     exit 1
 fi
 
-# Check for appimagetool
+# Check for appimagetool — pinned to a tagged release and SHA-256 verified before we exec it.
+# The old "continuous" tag is a moving, unverified network download that runs on the release
+# builder; verify it or refuse to package.
+APPIMAGETOOL_URL="https://github.com/AppImage/appimagetool/releases/download/1.9.0/appimagetool-x86_64.AppImage"
+APPIMAGETOOL_SHA256="46fdd785094c7f6e545b61afcfb0f3d98d8eab243f644b4b17698c01d06083d1"
 APPIMAGETOOL=""
 if command -v appimagetool &> /dev/null; then
-    APPIMAGETOOL="appimagetool"
-elif [ -f "${BUILD_DIR}/appimagetool-x86_64.AppImage" ]; then
-    APPIMAGETOOL="${BUILD_DIR}/appimagetool-x86_64.AppImage"
+    APPIMAGETOOL="appimagetool"   # maintainer's own trusted system install
 else
-    print_status "Downloading appimagetool..."
-    wget -q -O "${BUILD_DIR}/appimagetool-x86_64.AppImage" \
-        "https://github.com/AppImage/AppImageKit/releases/download/continuous/appimagetool-x86_64.AppImage"
-    chmod +x "${BUILD_DIR}/appimagetool-x86_64.AppImage"
-    APPIMAGETOOL="${BUILD_DIR}/appimagetool-x86_64.AppImage"
+    AT="${BUILD_DIR}/appimagetool-x86_64.AppImage"
+    if [ ! -f "$AT" ] || ! echo "${APPIMAGETOOL_SHA256}  ${AT}" | sha256sum -c --status; then
+        print_status "Downloading appimagetool 1.9.0 (pinned)..."
+        wget -q -O "$AT" "$APPIMAGETOOL_URL"
+        if ! echo "${APPIMAGETOOL_SHA256}  ${AT}" | sha256sum -c --status; then
+            print_error "appimagetool SHA-256 verification failed — refusing to use it"
+            rm -f "$AT"
+            exit 1
+        fi
+        chmod +x "$AT"
+    fi
+    APPIMAGETOOL="$AT"
 fi
 
 print_status "Creating AppDir structure..."