fix(ci): resolve libsodium pkg-config detection across all platforms

Add explicit SODIUM_USE_PKG_CONFIG control to all build targets:
- Linux amd64/arm64: Set SODIUM_USE_PKG_CONFIG=1 to force pkg-config detection
- Windows: Set SODIUM_USE_PKG_CONFIG=no to prevent conflict with SODIUM_LIB_DIR

Fixes build failures:
- Linux: "libsodium not found via pkg-config or vcpkg" despite libsodium-dev installed
- Windows: "SODIUM_LIB_DIR is incompatible with SODIUM_USE_PKG_CONFIG"
- ARM64: Same pkg-config detection issue as amd64

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitea/workflows/auto-tag.yml

@@ -344,6 +344,7 @@ jobs:
       - name: Build
         env:
           APPIMAGE_EXTRACT_AND_RUN: "1"
+          SODIUM_USE_PKG_CONFIG: "1"
         run: |
           npm ci --legacy-peer-deps
           CI=true npx tauri build --target x86_64-unknown-linux-gnu
@@ -446,6 +447,7 @@ jobs:
           OPENSSL_STATIC: "1"
           SODIUM_LIB_DIR: /usr/x86_64-w64-mingw32/lib
           SODIUM_STATIC: "1"
+          SODIUM_USE_PKG_CONFIG: "no"
         run: |
           npm ci --legacy-peer-deps
           CI=true npx tauri build --target x86_64-pc-windows-gnu
@@ -631,6 +633,7 @@ jobs:
           PKG_CONFIG_SYSROOT_DIR: /usr/aarch64-linux-gnu
           PKG_CONFIG_PATH: /usr/lib/aarch64-linux-gnu/pkgconfig
           PKG_CONFIG_ALLOW_CROSS: "1"
+          SODIUM_USE_PKG_CONFIG: "1"
           OPENSSL_NO_VENDOR: "0"
           OPENSSL_STATIC: "1"
           APPIMAGE_EXTRACT_AND_RUN: "1"