fix: drive the calorie estimate from reps with a duration floor

[Anexus5919]

📌 Related Issue

Fixes #877

---

📝 Description

estimateCalories accepted totalReps but computed calories purely from session duration (MET × weight × hours), so the rep count had no effect and an idle, long session out-scored an intense, short one. HistoryPage separately used totalReps × 1.5, so the summary and history estimates disagreed.

🔹 What has been changed?

• src/utils/calorieEstimator.ts: make work done the primary driver, keeping a duration floor for isometric holds:
  • calories = max(reps × 1.5 × (MET / default MET) × (weight / 70), MET × weight × hours) × accuracyMultiplier
  • The 1.5 kcal/rep base matches the per-rep convention already used in HistoryPage, so the two estimates are now consistent, and the existing label thresholds (30 / 100 / 200 kcal) stay meaningful.
  • The duration floor preserves time-based credit for holds (plank logs ~0 reps), so this is a strict improvement.
  • Non-finite/zero rep counts are treated as zero work.
• src/utils/__tests__/calorieEstimator.test.ts: unit tests.

🔹 Why are these changes needed?

• For a rep-counting fitness app, calories should reflect work done (reps), scaled by exercise intensity and body weight, not just wall-clock duration. This makes the estimate respond to reps and keeps the summary and history numbers consistent.

---

🛠️ Type of Change

• 🐛 Bug Fix

---

🧪 Testing

✅ Tests Performed

• Tested locally
• npx vitest run src/utils/__tests__/calorieEstimator.test.ts -> 9 tests pass (reps drive the result, MET scaling, weight scaling, accuracy multiplier, the duration floor for holds, the 1-calorie floor, default-MET fallback, NaN-rep guard).
• npx tsc --noEmit: changed files clean; npx eslint: 0 problems.

🌐 Browsers Tested

Not applicable (pure calculation logic; verified via unit tests).

---

📷 Screenshots / Demo (if applicable)

Not applicable.

---

📋 Checklist

• I have read the project's CONTRIBUTING guidelines
• My code follows the project style guidelines
• I have performed a self-review of my code
• I have tested my changes locally
• I have added/updated documentation where necessary (not applicable)
• My changes do not introduce new warnings or errors
• This PR is linked to an existing issue

---

💬 Additional Notes

Branched from latest upstream/main (5464425). A follow-up (not in this PR) could route HistoryPage's calorie filter through estimateCalories for a single source of truth.

[vercel]

@Anexus5919 is attempting to deploy a commit to the somiljain2024-4175's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Anexus5919]

@Somil450 @diksha78dev Kindly have a review on this pr. Thanks!