docs: add comment block explaining isometric projection math in layou… (JhaSourav07#956)

Closes JhaSourav07#376

## Description

Added an inline comment block in `lib/svg/layout.ts` right above the
`towers.push` statement to clearly explain the mathematical logic behind
the 2D-to-3D isometric projection grid mechanics and why the specific
scale values (300, 120, 16, 9) were chosen.
Fixes # 376

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [ ] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [ ] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [ ] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [ ] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07

lib/svg/layout.ts

@@ -103,6 +103,14 @@ export function computeTowers(
         ? `TODAY: ${day.date}: ${count} ${unit}`
         : `${day.date}: ${count} ${unit}`;
 
+      // Isometric projection: Maps 2D grid coordinates (i, j) to a 3D isometric screen space.
+      // - Origin: (300, 120) anchors the grid layout on the SVG canvas.
+      // - Indices: 'i' represents the week/column index; 'j' represents the day/row index.
+      // - Geometry:
+      //   * (i - j) * 16 handles the horizontal shift. Increasing 'i' moves right; increasing 'j' moves left.
+      //   * (i + j) * 9 handles the vertical depth. Both indices move the tile downward.
+      // - Constants: 16 and 9 represent half-widths and half-heights of the diamond tiles,
+      //   maintaining a clean ~2:1 aspect ratio for isometric perspective.
       towers.push({
         x: 300 + (i - j) * 16,
         y: 120 + (i + j) * 9,