ci(release): drop cross, use rustup targets + native linkers

cross spawns Docker containers per target, but the Gitea Actions
runner doesn't expose /var/run/docker.sock, so every cross-compile
step died with "Cannot connect to the Docker daemon".

Replace with rustup-installed targets plus per-target linker setup:
  - x86_64-gnu: native (no extra deps)
  - aarch64-gnu: gcc-aarch64-linux-gnu from apt
  - x86_64-musl: musl-tools from apt
  - aarch64-musl: rust-lld + link-self-contained (rust-std bundles
    musl libc.a + crt, no apt deps needed)

Verified aarch64-musl path locally: produces a statically linked
ARM aarch64 ELF.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/release.yaml

@@ -19,11 +19,19 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        target:
-          - x86_64-unknown-linux-gnu
-          - aarch64-unknown-linux-gnu
-          - x86_64-unknown-linux-musl
-          - aarch64-unknown-linux-musl
+        include:
+          - target: x86_64-unknown-linux-gnu
+            apt: ""
+            rustflags: ""
+          - target: aarch64-unknown-linux-gnu
+            apt: "gcc-aarch64-linux-gnu"
+            rustflags: ""
+          - target: x86_64-unknown-linux-musl
+            apt: "musl-tools"
+            rustflags: ""
+          - target: aarch64-unknown-linux-musl
+            apt: ""
+            rustflags: "-C linker=rust-lld -C link-self-contained=yes"
     steps:
       - uses: actions/checkout@v4
 
@@ -31,11 +39,16 @@ jobs:
         with:
           targets: ${{ matrix.target }}
 
+      - name: Install cross toolchain
+        if: matrix.apt != ''
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y --no-install-recommends ${{ matrix.apt }}
+
       - name: Cache cargo state
         uses: actions/cache@v4
         with:
           path: |
-            ~/.cargo/bin
             ~/.cargo/registry
             ~/.cargo/git
             target
@@ -43,14 +56,15 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-cargo-release-${{ matrix.target }}-
 
-      - name: Install cross
-        run: |
-          if ! command -v cross >/dev/null 2>&1; then
-            cargo install cross --locked --version 0.2.5
-          fi
-
-      - name: Cross-compile nuwiki-ls
-        run: cross build --release --target ${{ matrix.target }} -p nuwiki-ls
+      - name: Build nuwiki-ls
+        env:
+          # Per-target linker overrides. Cargo ignores the entries that
+          # don't match the current target, so setting all of them here
+          # keeps the matrix declarative.
+          CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER: aarch64-linux-gnu-gcc
+          CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_LINKER: musl-gcc
+          RUSTFLAGS: ${{ matrix.rustflags }}
+        run: cargo build --release --target ${{ matrix.target }} -p nuwiki-ls
 
       - name: Package archive
         id: package