Feat/add input validation bmi calculator

[thatperplextion]

📋 What does this PR do?

A clear summary of the changes made.

🔗 Related Issue

Closes #

🧪 How was this tested?

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📸 Screenshots (if UI changes)

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✅ Checklist

• I've read the CONTRIBUTING guide
• My code follows the project's style guidelines
• I've tested my changes locally
• I've linked the related issue
• I haven't introduced any new secrets or API keys

[Copilot]

Pull request overview

This PR improves client-side UX and robustness by adding input validation to the BMI calculator and replacing disruptive alert() error handling with in-app toast notifications, alongside some documentation cleanup and removal of client debug logging.

Changes:

• Add bounded validation + inline error display to BMICalculator.
• Replace alert(err.message) usage with a reusable Toast UI pattern across key pages.
• Add/expand JSDoc comments for several utilities and remove noisy client debug logs from ExercisePage.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
client/src/utils/rewardsUtils.js	Adds JSDoc; reviewed utility logic and flagged invalid-date handling in formatRelativeDate.
client/src/utils/normalizeProduct.js	Adds JSDoc clarifying normalization behavior for product identifiers.
client/src/utils/getAuthHeaders.js	Adds JSDoc describing dev-token vs Firebase token behavior (with a type syntax issue noted).
client/src/utils/formatters.js	Adds JSDoc for INR currency formatter.
client/src/pages/ProductPage.jsx	Adds toast notifications for cart-related errors instead of alert().
client/src/pages/NotesPage.jsx	Adds toast notification for empty-title validation instead of alert().
client/src/pages/HomePage.jsx	Adds toast notifications for cart operation failures instead of alert().
client/src/pages/ExercisePage.jsx	Removes client-side debug logging / warning noise.
client/src/components/BMICalculator.jsx	Adds bounded input validation and inline error rendering for BMI calculation.

Suppressed comments (2)

client/src/utils/rewardsUtils.js:72

• formatRelativeDate returns "NaN days ago" when dateValue cannot be parsed into a valid Date (e.g., invalid string). Add a validity check so invalid inputs return an empty string (or another safe fallback).

export const formatRelativeDate = (dateValue) => {
  if (!dateValue) return "";

  const date = new Date(dateValue);
  const today = new Date();

client/src/components/BMICalculator.jsx:57

• calculateBMI(w, h) is computed three times in a row. Compute it once and reuse the value to avoid duplicated work and ensure the displayed BMI, category, and recommendation are always derived from the exact same number.

    setResult({
      bmi: calculateBMI(w, h),
      category: getBMICategory(calculateBMI(w, h)),
      tdee: calculateTDEE(calculateBMR(w, h, a, formData.gender), activity),
      recommendation: getRecommendedCategory(calculateBMI(w, h)),
    });

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