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>

setup.sh

@@ -391,11 +391,26 @@ elif $SETUP_SAPLING; then
 
         SPEND_URL="https://z.cash/downloads/sapling-spend.params"
         OUTPUT_URL="https://z.cash/downloads/sapling-output.params"
+        # Consensus-critical MPC parameters with fixed, well-known SHA-256 (identical across every
+        # Zcash-family node; also pinned in scripts/build-lite-backend-artifact.sh). z.cash is
+        # plain HTTPS with no signature, so verify the digest and refuse a tampered/corrupt file.
+        SPEND_SHA256="8e48ffd23abb3a5fd9c5589204f32d9c31285a04b78096ba40a79b75677efc13"
+        OUTPUT_SHA256="2f0ebbcbb9bb0bcffe95a397e7eba89c29eb4dde6191c339db88570e3f3fb0e4"
 
-        curl -fSL -o "$PARAMS_DIR/sapling-spend.params"  "$SPEND_URL"  && \
-            ok "Downloaded sapling-spend.params"
-        curl -fSL -o "$PARAMS_DIR/sapling-output.params" "$OUTPUT_URL" && \
-            ok "Downloaded sapling-output.params"
+        if curl -fSL -o "$PARAMS_DIR/sapling-spend.params" "$SPEND_URL" \
+           && echo "${SPEND_SHA256}  $PARAMS_DIR/sapling-spend.params" | sha256sum -c --status; then
+            ok "Downloaded + verified sapling-spend.params"
+        else
+            rm -f "$PARAMS_DIR/sapling-spend.params"
+            err "sapling-spend.params download or SHA-256 verification failed — not installed"
+        fi
+        if curl -fSL -o "$PARAMS_DIR/sapling-output.params" "$OUTPUT_URL" \
+           && echo "${OUTPUT_SHA256}  $PARAMS_DIR/sapling-output.params" | sha256sum -c --status; then
+            ok "Downloaded + verified sapling-output.params"
+        else
+            rm -f "$PARAMS_DIR/sapling-output.params"
+            err "sapling-output.params download or SHA-256 verification failed — not installed"
+        fi
     fi
 else
     skip "Sapling params not found (use --sapling to download, or they'll be extracted at runtime from embedded builds)"