fix(layout): resolve isometric tile height mismatch between projectIsometric (10) and renderIsometricLabels (9) — move grid constants to layoutConstants.ts

[ChetanSenta]

Description

Fixes #5610

Pillar

• 📐 Pillar 2 — Geometric SVG Improvement
• 🎨 Pillar 1 — New Theme Design
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix)

Visual Preview

Fixes label drift on badges using ?labels=true — month and weekday
labels now align correctly with their tower columns, especially
visible on the rightmost columns of ?size=large&labels=true badges.

Root cause

projectIsometric() in layout.ts used TILE_HEIGHT_HALF = 10.
renderIsometricLabels() in generator.ts used TILE_HEIGHT_HALF = 9.

Over 14 columns (max rendered window):
accumulated y-drift = (10 - 9) × 14 = 14px

Changes

File	Change
lib/svg/layoutConstants.ts	Added 4 grid constants: GRID_ORIGIN_X, GRID_ORIGIN_Y, TILE_WIDTH_HALF, TILE_HEIGHT_HALF=10
lib/svg/layout.ts	projectIsometric() now uses imported constants instead of magic numbers
lib/svg/generator.ts	renderIsometricLabels() deleted local constant block (was 9), now imports TILE_HEIGHT_HALF=10
lib/svg/layout.test.ts	7 new regression tests including explicit guard against the 9 vs 10 reversion

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally.
• I have run npm run format and npm run lint locally and resolved all errors.
• My commits follow the Conventional Commits format.
• I have updated README.md if I added a new theme or URL parameter.
• I have starred the repo.
• 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.
• (Recommended) I joined the CommitPulse Discord server.

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[github-actions]

📦 Next.js Bundle Size Report (Gzipped Sizes)

✨ No significant bundle size changes detected.

📊 Summary of Totals

Category	PR Size	Base Size	Difference
Total JS	3694.34 KB	3694.34 KB	0 B
Total CSS	296.06 KB	296.06 KB	0 B

[Aamod-Dev]

Review Summary

Labels applied:

• level:intermediate — Touches 8 files with both a core bug fix (TILE_HEIGHT_HALF mismatch: 10 vs 9), scaling parameter adjustments (LOG_SCALE_MULTIPLIER 12→15, MAX_LOG_HEIGHT 80→50), test reorganization, and a vitest config change. Requires understanding of isometric projection math across layout.ts and generator.ts.
• quality:clean — Root cause is clearly identified and explained: accumulated 14px y-drift over 14 columns (layoutConstants.ts:28-31). Tests include explicit guards against the 9 vs 10 reversion (layout.test.ts:428-434). The scaling parameter changes are documented and test assertions updated accordingly.
• type:bug — Fixes label drift on ?labels=true badges caused by TILE_HEIGHT_HALF mismatch between projectIsometric() and
  enderIsometricLabels().
• type:refactor — Extracted isometric grid constants to layoutConstants.ts as single source of truth.
• type:testing — 7 new regression tests for projectIsometric verifying coordinate math.

Mentor: Aamod007

Assessment: Solid bug fix with thorough root cause analysis. The extracted constants pattern prevents future drift. The scaling parameter changes (LOG_SCALE_MULTIPLIER, MAX_LOG_HEIGHT) are a notable scope addition beyond the title — please confirm these adjustments are intentional and don't affect existing badge output heights.

Approved! 🚀