chore: centralize deploy/install CD actions in twentyhq/twenty (#19454)

## Summary

- Adds `deploy-twenty-app` and `install-twenty-app` composite actions to
`.github/actions/` so app repos can reference them remotely — same
pattern as `spawn-twenty-app-dev-test` for CI
- Updates `cd.yml` in template, hello-world, and postcard to use
`twentyhq/twenty/.github/actions/deploy-twenty-app@main` /
`install-twenty-app@main` instead of local `./.github/actions/` copies
- Removes the 6 local action files that were duplicated across template
and example apps

**Before** (each app repo carried its own action copies):
```yaml
uses: ./.github/actions/deploy
```

**After** (centralized, like CI):
```yaml
uses: twentyhq/twenty/.github/actions/deploy-twenty-app@main
```


Made with [Cursor](https://cursor.com)

.github/actions/deploy-twenty-app/action.yml

@@ -0,0 +1,46 @@
+name: Deploy Twenty App
+description: Build and deploy a Twenty app to a remote instance
+
+inputs:
+  api-url:
+    description: Base URL of the target Twenty instance (e.g. https://my.twenty.instance)
+    required: true
+  api-key:
+    description: API key or access token for the target instance
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - name: Enable Corepack
+      shell: bash
+      run: corepack enable
+
+    - name: Setup Node.js
+      uses: actions/setup-node@v4
+      with:
+        node-version-file: '.nvmrc'
+        cache: yarn
+
+    - name: Install dependencies
+      shell: bash
+      run: yarn install --immutable
+
+    - name: Configure remote
+      shell: bash
+      run: |
+        mkdir -p ~/.twenty
+        node -e "
+          const fs = require('fs'), path = require('path'), os = require('os');
+          fs.writeFileSync(path.join(os.homedir(), '.twenty', 'config.json'), JSON.stringify({
+            version: 1,
+            remotes: { target: { apiUrl: process.env.API_URL, apiKey: process.env.API_KEY } }
+          }, null, 2));
+        "
+      env:
+        API_URL: ${{ inputs.api-url }}
+        API_KEY: ${{ inputs.api-key }}
+
+    - name: Deploy
+      shell: bash
+      run: yarn twenty deploy --remote target

.github/actions/install-twenty-app/action.yml

@@ -0,0 +1,46 @@
+name: Install Twenty App
+description: Install (or upgrade) a Twenty app on a specific workspace
+
+inputs:
+  api-url:
+    description: Base URL of the target Twenty instance (e.g. https://my.twenty.instance)
+    required: true
+  api-key:
+    description: API key or access token for the target workspace
+    required: true
+
+runs:
+  using: composite
+  steps:
+    - name: Enable Corepack
+      shell: bash
+      run: corepack enable
+
+    - name: Setup Node.js
+      uses: actions/setup-node@v4
+      with:
+        node-version-file: '.nvmrc'
+        cache: yarn
+
+    - name: Install dependencies
+      shell: bash
+      run: yarn install --immutable
+
+    - name: Configure remote
+      shell: bash
+      run: |
+        mkdir -p ~/.twenty
+        node -e "
+          const fs = require('fs'), path = require('path'), os = require('os');
+          fs.writeFileSync(path.join(os.homedir(), '.twenty', 'config.json'), JSON.stringify({
+            version: 1,
+            remotes: { target: { apiUrl: process.env.API_URL, apiKey: process.env.API_KEY } }
+          }, null, 2));
+        "
+      env:
+        API_URL: ${{ inputs.api-url }}
+        API_KEY: ${{ inputs.api-key }}
+
+    - name: Install
+      shell: bash
+      run: yarn twenty install --remote target