Add self-documenting make help target and reusable Makefile skill

[vlantonov]

Summary

Developers cloning the project had no discoverable way to learn what make targets were available without reading the Makefile directly. This PR adds a help target that auto-generates a target listing from inline ## description comments, making the project more approachable for new contributors and portfolio viewers. It also packages the pattern as a reusable Copilot skill so the same workflow can be applied to other Makefiles in one command.

Motivation / Context

• Addresses the onboarding usability gap: bare make previously defaulted to build with no usage guidance.
• No linked issue; change is self-contained and additive.
• Known limitation: the grep pattern matches single-colon rules only; double-colon rules (target:: ## …) would require a pattern adjustment.

What Changed

Build tooling (Makefile)

• Added help target with grep/awk recipe that prints all ## description-annotated targets in colour-coded, aligned columns.
• Set .DEFAULT_GOAL := help so bare make prints usage instead of building.
• Added ## description inline comments to all five existing targets (build, test, vet, clean, run).
• Added help to the .PHONY declaration.

Developer tooling (makefile-help)

• New SKILL.md: VS Code Copilot on-demand skill (/makefile-help) with a 4-step procedure — read, annotate, insert, validate.
• New assets/help-target.mk: reusable drop-in Makefile snippet bundled with the skill.

How It Was Tested / Verified

• make help — all 6 targets listed with correct descriptions (output captured below).
• make build — compiles cleanly, no new warnings.
• make test — all 5 package test suites pass with -race flag (config, grid, robot, simulation, tui).
• make vet — no issues reported.
• No existing recipe lines were modified; diff confirms recipe preservation.

Screenshots / Output Samples

Usage:
  make <target>

Targets:
  build                Compile the binary
  clean                Remove compiled binary
  help                 Show this help message
  run                  Run the robot demo
  test                 Run all tests with race detector
  vet                  Run go vet on all packages

Checklist

• Builds cleanly with the project's standard build configuration
• Tests pass locally
• Documentation / README updated if behavior or usage changed — make help is self-documenting; README make section can optionally reference make help in a follow-up
• No new warnings introduced by the configured toolchain/checks