Restrict @types/node to 20.x in dependabot for templates (#3505)

Prevent dependabot from proposing major version updates for
`@types/node` beyond 20.x to maintain Node.js 20 LTS compatibility.

## Changes

- Added ignore rule in templates npm ecosystem to block `@types/node`
major version updates
- Minor and patch updates within 20.x remain allowed (e.g., 20.12.0 →
20.15.0)

```yaml
# TypeScript templates (any package.json in templates/)
- package-ecosystem: "npm"
  directories:
    - "/templates/**"
  # ...
  ignore:
    # Keep @types/node at 20.x.x for backward compatibility
    # Node.js 20 is LTS and we want to ensure compatibility
    - dependency-name: "@types/node"
      update-types: ["version-update:semver-major"]
```

This prevents updates like 20.x.x → 21.x.x while allowing 20.12.0 →
20.15.0.

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<!-- CURSOR_SUMMARY -->
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> [!NOTE]
> **Low Risk**
> Config-only change affecting Dependabot update policy; no application
code or runtime behavior is modified.
> 
> **Overview**
> Dependabot is updated to **ignore major-version updates** for
`@types/node` in the templates `npm` ecosystem, effectively keeping it
pinned to the Node 20 type definitions for backward compatibility.
> 
> No runtime/build logic changes; this only adjusts automated dependency
update behavior.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
3fdcae3. This will update automatically
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---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: callicles <4429209+callicles@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -31,6 +31,11 @@ updates:
         patterns:
           - "@514labs/moose-cli"
           - "@514labs/moose-lib"
+    ignore:
+      # Keep @types/node at 20.x.x for backward compatibility
+      # Node.js 20 is LTS and we want to ensure compatibility
+      - dependency-name: "@types/node"
+        update-types: ["version-update:semver-major"]
 
   # Python templates (any requirements.txt in templates/)
   - package-ecosystem: "pip"