Add build checks and improve existing CI/CD checks

Run quality checks for every possible OS because behavior of linting
rules may change per OS (e.g. `linebreak-style` ESLint assertment varies
by Unix-like vs Windows).

Add a new check to ensure project can be built:
  1. As both web and desktop applications.
    Different jobs are used due to nonidentical environment/mode support.
    Reference: nklayman/vue-cli-plugin-electron-builder#1627.
  2. Targeting all possible modes.
    The modes are configured using `--mode` but electron CLI checks
    `NODE_ENV` so it's set as well.
    Reference: nklayman/vue-cli-plugin-electron-builder#1626.

  3. On and for different operating systems.

Fix typo "Run units" instead of "Run unit tests".

Link to specific GitHub actions page for workflow runs.

Update documentation to match new structure, and change nontransparent
icons from the diagram and consistently use imperative for actions.

Rename `release-site` , `release-git`, `release-desktop` to
`site-release` , `git-release` and `desktop-release` to not be Yoda.

.github/workflows/checks.build.yaml

@@ -0,0 +1,59 @@
+name: build-checks
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build-web:
+    strategy:
+      matrix:
+        os: [ macos, ubuntu, windows ]
+        mode: [ development, test, production ]
+      fail-fast: false # Allows to see results from other combinations
+    runs-on: ${{ matrix.os }}-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Setup node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 15.x
+      -
+        name: Install dependencies
+        run: npm ci
+      -
+        name: Build
+        run: npm run build -- --mode ${{ matrix.mode }}
+
+  # A new job is used due to environments/modes different from Vue CLI, https://github.com/nklayman/vue-cli-plugin-electron-builder/issues/1626
+  build-desktop:
+    strategy:
+      matrix:
+        os: [ macos, ubuntu, windows ]
+        mode: [ development, production ] # "test" is not supported https://github.com/nklayman/vue-cli-plugin-electron-builder/issues/1627
+      fail-fast: false # Allows to see results from other combinations
+    runs-on: ${{ matrix.os }}-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Setup node
+        uses: actions/setup-node@v1
+        with:
+          node-version: 15.x
+      -
+        name: Install dependencies
+        run: npm ci
+      -
+        name: Install cross-env
+        # Used to set NODE_ENV due to https://github.com/nklayman/vue-cli-plugin-electron-builder/issues/1626
+        run: npm install --global cross-env
+      -
+        name: Build
+        run: |-  
+          cross-env-shell NODE_ENV=${{ matrix.mode }}
+          npm run electron:build -- --publish never --mode ${{ matrix.mode }}