fix(ui): implement exact absolute coordinate alignment for month labels on heatmap

[Visaka123]

Summary

This PR addresses and resolves structural alignment anomalies affecting the **ContributionHeatmap** month timeline headers. The original implementation relied on fluid layout constraints and implicit element distributions, leading to rendering drift and text truncation when months initiated mid-week or crossed chronological year boundaries.

This refactor establishes a deterministic positioning matrix that maps text headers directly to the exact grid track indices utilized by the underlying canvas architecture.

Closes #249

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Refactor / code cleanup (non-breaking optimization)

Changes Made

1. Chronological State Transition Engine

• Replaced unstable day-of-month fallback matching (cell.date.getDate() === 1) with an itemized matrix traversal check utilizing a strict unique tracking set (!seenMonths.has(monthKey)).
• This ensures that a month column anchor is initialized the absolute instant a week track encounters the first valid day of a new month, completely normalizing rendering behaviors across tricky mid-week switches.

2. Matrix Coordinate Harmonization

• Migrated the header row away from standard CSS flex/grid track distributions to prevent dynamic column compression.
• Established an identical coordinate identity rule where each label's horizontal positioning is strictly computed via the canvas baseline formula:
  LABEL_WIDTH + weekIndex * (CELL_SIZE + CELL_GAP)
• This binds text anchors directly to the starting pixel coordinate of their matching column tracks.

3. Allocation and Truncation Guard

• Applied width: "auto" and min-width: "max-content" layers to the absolute layout blocks to eliminate multi-column tracking collisions. Short-span labels (e.g., Jun, Jul) bleed naturally into subsequent empty tracking headers without visual string truncation (...).
• Extracted and memoized the Intl.DateTimeFormat instance globally. This removes redundant engine instantiations inside the raw loop iterations, significantly reducing garbage collection overhead and main-thread execution time.
• Cleaned up active layout tracing logs (console.log) to keep production runtime terminal spaces pristine.

How to Test

1. Initialize the local development environment (npm run dev).
2. Verify that month markers left-align flawlessly with the exact geometric boundary of their corresponding grid track columns.
3. Inspect boundary edge-cases (specifically January crossing the year boundary line and April/May mid-week starting points) to confirm mathematical alignment.
4. Verify through the browser inspection console that zero infinite layout re-render loops or network rate-limit errors occur.

Screenshots

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff

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[Priyanshu-byte-coder]

Fix is correct — switching from grid-based to absolute positioning for month labels solves the alignment problem. The gridRow reindex, setLastUpdated moved to .then(), and totalGridWidth calculation are all sound. One note for follow-up: clean up the hyperbolic comments ("100% MATHEMATICALLY PRECISE...") — not production style. Merging.