fix(ci): unset SODIUM_USE_PKG_CONFIG and use SODIUM_LIB_DIR in auto-tag.yml

The libsodium-sys-stable build.rs panics when both SODIUM_LIB_DIR and
SODIUM_USE_PKG_CONFIG are set simultaneously. The runner environment at
172.0.0.29 has SODIUM_USE_PKG_CONFIG set (not traceable to any workflow
file or Docker image ENV layer), which conflicts with any step that sets
SODIUM_LIB_DIR.

For all three platform builds (linux-amd64, windows-amd64, linux-arm64):
- Add `unset SODIUM_USE_PKG_CONFIG` to the shell before cargo runs
- Switch Linux builds from inline apt-get to SODIUM_LIB_DIR (Docker
  images already include libsodium-dev, removing the redundant install)
- Extend arm64 PKG_CONFIG_PATH to include /usr/aarch64-linux-gnu/lib/pkgconfig
  (matching the beta workflow for consistency)

The unset is a no-op when the variable is absent; it cleanly clears any
ambient value injected by the runner infrastructure.

.gitea/workflows/auto-tag.yml

@@ -344,8 +344,9 @@ jobs:
       - name: Build
         env:
           APPIMAGE_EXTRACT_AND_RUN: "1"
+          SODIUM_LIB_DIR: /usr/lib/x86_64-linux-gnu
         run: |
-          apt-get update -qq && apt-get install -y --no-install-recommends libsodium-dev
+          unset SODIUM_USE_PKG_CONFIG
           npm ci --legacy-peer-deps
           CI=true npx tauri build --target x86_64-unknown-linux-gnu
       - name: Upload artifacts
@@ -448,6 +449,7 @@ jobs:
           SODIUM_LIB_DIR: /usr/x86_64-w64-mingw32/lib
           SODIUM_STATIC: "1"
         run: |
+          unset SODIUM_USE_PKG_CONFIG
           npm ci --legacy-peer-deps
           CI=true npx tauri build --target x86_64-pc-windows-gnu
       - name: Upload artifacts
@@ -630,13 +632,14 @@ jobs:
           AR_aarch64_unknown_linux_gnu: aarch64-linux-gnu-ar
           CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER: aarch64-linux-gnu-gcc
           PKG_CONFIG_SYSROOT_DIR: /usr/aarch64-linux-gnu
-          PKG_CONFIG_PATH: /usr/lib/aarch64-linux-gnu/pkgconfig
+          PKG_CONFIG_PATH: /usr/lib/aarch64-linux-gnu/pkgconfig:/usr/aarch64-linux-gnu/lib/pkgconfig
           PKG_CONFIG_ALLOW_CROSS: "1"
           OPENSSL_NO_VENDOR: "0"
           OPENSSL_STATIC: "1"
           APPIMAGE_EXTRACT_AND_RUN: "1"
+          SODIUM_LIB_DIR: /usr/lib/aarch64-linux-gnu
         run: |
-          apt-get update -qq && apt-get install -y --no-install-recommends libsodium-dev:arm64
+          unset SODIUM_USE_PKG_CONFIG
           npm ci --legacy-peer-deps
           CI=true npx tauri build --target aarch64-unknown-linux-gnu --bundles deb,rpm
       - name: Upload artifacts