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>

CMakeLists.txt

@@ -53,7 +53,6 @@ set_property(CACHE DRAGONX_LITE_BACKEND_LINK_MODE PROPERTY STRINGS imported)
 set(DRAGONX_LITE_BACKEND_ABI "sdxl-c-v1" CACHE STRING "Expected lite backend C ABI version")
 set(DRAGONX_LITE_BACKEND_SYMBOLS_FILE "" CACHE FILEPATH "Path to generated lite backend exported-symbol inventory")
 set(DRAGONX_LITE_BACKEND_MANIFEST "" CACHE FILEPATH "Optional path to generated lite backend artifact manifest")
-option(DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE "Require verified signature metadata in the lite backend artifact manifest" OFF)
 set(DRAGONX_LITE_BACKEND_REQUIRED_SYMBOLS
     litelib_wallet_exists
     litelib_initialize_new
@@ -126,31 +125,12 @@ if(DRAGONX_ENABLE_LITE_BACKEND)
     if(DRAGONX_LITE_BACKEND_MANIFEST AND NOT EXISTS "${DRAGONX_LITE_BACKEND_MANIFEST}")
         message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST does not exist: ${DRAGONX_LITE_BACKEND_MANIFEST}")
     endif()
-    if(DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE)
-        if(NOT DRAGONX_LITE_BACKEND_MANIFEST)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires DRAGONX_LITE_BACKEND_MANIFEST")
-        endif()
-        file(READ "${DRAGONX_LITE_BACKEND_MANIFEST}" DRAGONX_LITE_BACKEND_MANIFEST_JSON)
-        string(JSON DRAGONX_LITE_SIGNATURE_STATUS ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_STATUS_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verification_status)
-        if(DRAGONX_LITE_SIGNATURE_STATUS_ERROR)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST is missing signature verification status")
-        endif()
-        if(NOT DRAGONX_LITE_SIGNATURE_STATUS STREQUAL "verified")
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires verified signature metadata")
-        endif()
-        string(JSON DRAGONX_LITE_SIGNATURE_VERIFIED_SHA ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_VERIFIED_SHA_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verified_artifact_sha256)
-        string(JSON DRAGONX_LITE_ARTIFACT_SHA ERROR_VARIABLE DRAGONX_LITE_ARTIFACT_SHA_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" artifact sha256)
-        if(DRAGONX_LITE_SIGNATURE_VERIFIED_SHA_ERROR OR DRAGONX_LITE_ARTIFACT_SHA_ERROR)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST is missing artifact/signature SHA-256 metadata")
-        endif()
-        if(NOT DRAGONX_LITE_SIGNATURE_VERIFIED_SHA STREQUAL DRAGONX_LITE_ARTIFACT_SHA)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_MANIFEST signature metadata does not verify the artifact SHA-256")
-        endif()
-        string(JSON DRAGONX_LITE_SIGNATURE_PERFORMED ERROR_VARIABLE DRAGONX_LITE_SIGNATURE_PERFORMED_ERROR GET "${DRAGONX_LITE_BACKEND_MANIFEST_JSON}" signature_verification verification_performed)
-        if(DRAGONX_LITE_SIGNATURE_PERFORMED_ERROR OR NOT DRAGONX_LITE_SIGNATURE_PERFORMED)
-            message(FATAL_ERROR "DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE requires verification_performed=true")
-        endif()
-    endif()
+    # Note (F15-1): the former signature-metadata gate was removed. It trusted a
+    # "verification_status: verified" field that scripts/build-lite-backend-artifact.sh
+    # self-attested with no cryptographic check (the "verified" SHA was just the artifact's
+    # own SHA). The trust root is now build-from-source: that script builds the backend from
+    # the vendored in-tree source and refuses prebuilt artifacts, so the library linked here
+    # is the one built from reviewed source. The required-symbol inventory check above stays.
 
     add_library(dragonx_lite_backend UNKNOWN IMPORTED)
     set_target_properties(dragonx_lite_backend PROPERTIES
@@ -1204,5 +1184,5 @@ message(STATUS "  Lite backend:   ${DRAGONX_LITE_BACKEND_READY}")
 message(STATUS "  Lite lib:       ${DRAGONX_LITE_BACKEND_LIBRARY}")
 message(STATUS "  Lite symbols:   ${DRAGONX_LITE_BACKEND_SYMBOLS_FILE}")
 message(STATUS "  Lite manifest:  ${DRAGONX_LITE_BACKEND_MANIFEST}")
-message(STATUS "  Lite signature: ${DRAGONX_LITE_BACKEND_REQUIRE_SIGNATURE}")
+message(STATUS "  Lite trust:     built-from-source (vendored third_party/silentdragonxlite)")
 message(STATUS "")