Refactor Android CI workflow to use Nix actions and improve translation file collection

.github/actions/nix-devshell/action.yml

@@ -0,0 +1,87 @@
+name: "nix-devshell"
+description:
+  "Set up Nix, optionally cache, prebuild the devshell and run commands inside
+  the devshell."
+inputs:
+  prebuild:
+    description:
+      "Whether to prebuild the devshell (nix develop --command true)."
+    required: false
+    default: "false"
+  commands:
+    description:
+      "Commands to run inside the devshell (executed with bash -lc)."
+    required: false
+    default: ""
+  cache:
+    description:
+      "Enable caching for Nix artifacts (caches ~/.cache/nix and
+      ~/.local/share/nix)."
+    required: false
+    default: "true"
+  cache-key-files:
+    description: "Files to hash for cache key (glob). Default is 'flake.lock'."
+    required: false
+    default: "flake.lock"
+  cachix-name:
+    description: "Optional Cachix cache name to use (requires cachix token)."
+    required: false
+    default: ""
+  cachix-token:
+    description: "Optional Cachix token (pass via secrets)."
+    required: false
+    default: ""
+
+runs:
+  using: "composite"
+  steps:
+    - name: Install Nix (idempotent)
+      shell: bash
+      run: |
+        set -euo pipefail
+        if ! command -v nix >/dev/null 2>&1; then
+          curl -L https://nixos.org/nix/install | sh -s -- --no-daemon
+        fi
+        # source the nix profile if present
+        if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+          . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+        fi
+        nix --version
+
+    - name: Setup Cachix (optional)
+      if: ${{ inputs.cachix-name != '' && inputs.cachix-token != '' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        curl -L https://cachix.org/api/install | sh
+        cachix use --token "${{ inputs.cachix-token }}" "${{ inputs.cachix-name }}"
+
+    - name: Cache Nix directories
+      if: ${{ inputs.cache == 'true' }}
+      uses: actions/cache@v4
+      with:
+        path: |
+          ~/.cache/nix
+          ~/.local/share/nix
+        key: ${{ runner.os }}-nix-${{ hashFiles(inputs.cache-key-files) }}
+        restore-keys: ${{ runner.os }}-nix-
+
+    - name: Prebuild devshell
+      if: ${{ inputs.prebuild == 'true' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+          . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+        fi
+        nix --extra-experimental-features 'nix-command flakes' develop --command true
+
+    - name: Run commands in devshell
+      if: ${{ inputs.commands != '' }}
+      shell: bash
+      run: |
+        set -euo pipefail
+        if [ -f "$HOME/.nix-profile/etc/profile.d/nix.sh" ]; then
+          . "$HOME/.nix-profile/etc/profile.d/nix.sh"
+        fi
+        nix --extra-experimental-features 'nix-command flakes' develop --command bash -lc "${{ inputs.commands }}"