[Secondary] Refactor Grid System from Quad/Square to Hexagonal Tiles

[MeriAlguero]

[Secondary] Refactor Grid System from Quad/Square to Hexagonal Tiles

Priority: Secondary / Refactor
Labels: refactor, grid, gameplay, secondary

Summary

Refactor the current square/quad 8x8 grid into a hexagonal grid system. Update tile spawning, spatial layout, neighbor detection, and distance calculations to use hex coordinates (axial or cube coordinates).

Tasks

• Replace square cube tiles with 3D Hexagon primitive models or procedural hex meshes.
• Update grid generation logic (GridManager) to offset odd/even rows (or columns) using point-top or flat-top hexagon layout spacing.
• Update tile coordinate tracking from standard Cartesian $(X, Y)$ to Hexagonal Axial $(q, r)$ or Cube $(q, r, s)$ coordinates.
• Replace Manhattan distance calculation with Hexagonal distance formula:
  Distance = (Abs(q1 - q2) + Abs(r1 - r2) + Abs(s1 - s2)) / 2
• Update target tile highlighting and unit movement to validate paths across 6 adjacent hex directions instead of 4/8 quad directions.

Acceptance Criteria

• Grid spawns as a seamlessly aligned hexagonal layout without overlapping or gaps.
• Selecting a player highlights valid movement hexes based on 6-directional movement.
• Hex distance math correctly restricts movement range according to character movement stats.
• Unit positioning correctly snaps to the center of target hex tiles.