chore: update immutable package to ^5.1.5

[mi5t4n]

This PR updates the immutable package to ^5.1.5 using overrides.

Resolves

1. https://github.com/rtCamp/rtMedia/security/dependabot/125
2. https://github.com/rtCamp/rtMedia/security/dependabot/124

[gemini-code-assist]

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[Copilot]

Pull request overview

Updates the repo’s npm dependency resolution to force immutable to ^5.1.5 via overrides, and refreshes the lockfile so installs resolve to immutable@5.1.5.

Changes:

• Add an npm overrides entry for immutable at ^5.1.5.
• Update package-lock.json to reflect immutable resolving to 5.1.5.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
package.json	Adds immutable to npm overrides to enforce the desired resolved version.
package-lock.json	Updates the resolved immutable package metadata to 5.1.5.

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