Add workflows for linting and syncing subtrees.json

src/phreeqcpp/.github/subtrees.json

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+[
+  {
+    "prefix": "common",
+    "url": "git@${CI_SERVER_HOST}:${GROUP}-subtrees/phreeqc3-src-common.git"
+  }
+]

src/phreeqcpp/.github/workflows/lint-subtrees.yml

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+# This workflow lints the subtrees.json file to ensure it is valid and up-to-date.
+# It is triggered on pull requests that modify the subtrees.json file or can be run manually
+# via the GitHub Actions UI.
+name: Lint subtrees.json
+
+on:
+  pull_request:
+    paths:
+      - '.github/subtrees.json'
+  workflow_call:
+  workflow_dispatch:
+
+jobs:
+  lint-subtrees:
+    runs-on: ubuntu-latest
+    env:
+      CI_SERVER_HOST: github.com
+      GROUP: usgs-coupled
+    steps:
+      - uses: usgs-coupled/sync-subtrees-action/lint-subtrees/@main
+        with:
+          ssh-private-key: ${{ secrets.SSH_PRIVATE_KEY }}

src/phreeqcpp/.github/workflows/subtree.yml

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+name: Sync Subtrees
+
+on:
+  workflow_dispatch:
+    inputs:
+      dryRun:
+        description: 'If true, don’t push any changes (for testing only).'
+        required: true
+        default: true
+        type: boolean
+      testMerge:
+        description: 'Run in test mode, pushing to a test branch.'
+        required: true
+        default: false
+        type: boolean
+
+jobs:
+  sync-subtrees:
+    runs-on: ubuntu-latest
+    env:
+      CI_SERVER_HOST: github.com
+      GROUP: usgs-coupled    
+    steps:
+      - name: Run sync-subtrees-action
+        uses: usgs-coupled/sync-subtrees-action@main
+        with:
+          dryRun: ${{ inputs.dryRun }}
+          testMerge: ${{ inputs.testMerge }}
+          repository_name: ${{ github.event.repository.name }}
+          default_branch: ${{ github.event.repository.default_branch }}
+          run_number: ${{ github.run_number }}
+          ssh_private_key: ${{ secrets.SSH_PRIVATE_KEY }}