feat(lite): vendor SDXL backend source; source deps from git.dragonx.is

Vendor the two local Rust crates that build the lite backend artifact into
third_party/silentdragonxlite/ (the qtlib C-ABI wrapper + the silentdragonxlitelib
core, with proto/res and all the lite-send fixes), and point
build-lite-backend-artifact.sh's default --backend-dir there, so the lite wallet
builds without the upstream SilentDragonXLite repo.

External build inputs are now only the Rust toolchain + git.dragonx.is + crates.io:
- the 6 librustzcash git deps point at the git.dragonx.is/DragonX/librustzcash
  mirror (pinned rev acff1444), not git.hush.is;
- the Sapling params are gitignored (not committed, no Git LFS) - the build fetches
  them from the git.dragonx.is/DragonX/zcash-params 'sapling-v1' release and verifies
  their SHA-256 before rust-embed bakes them in (ensure_sapling_params).

For fully offline builds, cargo vendor into lib/vendor/ and add a vendored-sources
redirect (vendor/ is gitignored; the script symlinks it into the prepared dir).

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

CLAUDE.md

@@ -61,7 +61,7 @@ There is no per-test filtering — it is one binary that runs every assertion. T
 
 Variants are selected with CMake options (set by `build.sh` flags), surfaced to C++ as compile definitions:
 - `DRAGONX_BUILD_LITE` (`--lite`) → `DRAGONX_LITE_BUILD` define; renames the app to `ObsidianDragonLite` and excludes embedded-daemon / full-node assets (Sapling params, asmap, dragonxd).
-- `DRAGONX_ENABLE_LITE_BACKEND` → links a real external lite backend. Requires `--lite`, link mode `imported`, ABI `sdxl-c-v1`, and a symbols inventory file (built by `scripts/build-lite-backend-artifact.sh`); CMake hard-fails if any required `litelib_*` symbol is missing.
+- `DRAGONX_ENABLE_LITE_BACKEND` → links a real external lite backend. Requires `--lite`, link mode `imported`, ABI `sdxl-c-v1`, and a symbols inventory file (built by `scripts/build-lite-backend-artifact.sh`); CMake hard-fails if any required `litelib_*` symbol is missing. The backend **source is vendored in-tree** at `third_party/silentdragonxlite/` — the `qtlib` C-ABI wrapper (`lib/`, produces `libsilentdragonxlite.a`) and the `silentdragonxlitelib` core (`silentdragonxlite-cli/lib/`, with `proto/` + `res/`). `build-lite-backend-artifact.sh` defaults `--backend-dir` there, so the lite wallet builds **without** the upstream SilentDragonXLite repo. External build inputs are limited to the **Rust toolchain (rustc/cargo 1.63)** plus two project-controlled sources on `git.dragonx.is`: the librustzcash crates come from the mirror `git.dragonx.is/DragonX/librustzcash` (the 6 `git =` deps in the core `Cargo.toml`, pinned to rev `acff1444…`), and the **Sapling params are not committed** (gitignored) — the build fetches them from the `git.dragonx.is/DragonX/zcash-params` release `sapling-v1` and verifies their SHA-256 before rust-embed bakes them in (`ensure_sapling_params`; override the URL with `SAPLING_PARAMS_BASE_URL`). Other crate deps come from crates.io. For a fully offline build, `cargo vendor` into `third_party/silentdragonxlite/lib/vendor/` and add a `vendored-sources` redirect to `lib/.cargo/config.toml` (the build script symlinks `vendor/` into its prepared dir if present); `vendor/` is gitignored.
 - `DRAGONX_ENABLE_CHAT` → `DRAGONX_ENABLE_CHAT` define gating the chat module.
 
 Guard full-node-only code paths with `#if DRAGONX_LITE_BUILD` / chat code with `DRAGONX_ENABLE_CHAT`.