feat(utils): add browser-safe runtime environment detection utility (#128)

[Code-Paragon]

This PR resolves #128 by introducing a browser-safe runtime environment detection utility (isNode, isBrowser, isReactNative) that safely checks for execution contexts without triggering ReferenceErrors in cross-platform environments (Node, browser, or React Native).

Linked Issue

Closes #128

Type of Change

• ✨ New Feature (minor)

Changes Made

• src/utils/env.ts:
  • Implemented defensive environment checks (isNode, isBrowser, and isReactNative) guarding against undefined globals like process, window, document, and navigator.
• src/utils/index.ts & src/index.ts:
  • Exported environment detection utilities from package root.
• tests/env.test.ts:
  • Added unit tests verifying safe behavior across simulated Node, browser, and React Native runtimes using Vitest global stubs.
• vitest.config.ts -> vitest.config.mts:
  • Renamed config to .mts for native ES module resolution on Windows.

Acceptance Criteria Checklist

• An environment detection utility is added.
• The utility works safely in Node, browser, and React Native-like contexts.
• Tests cover expected runtime detection cases.
• Documentation explains intended usage.

Checklist

• I have read CONTRIBUTING.md
• This PR is linked to an open issue (Add browser-safe environment detection utility #128)
• Code conforms to project formatting guidelines

[El-swaggerito]

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Please update the branch with the latest base branch, resolve the conflicts, and fix the failing workflow checks.

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