Set up dev environment: AGENTS.md + toolchain notes

[sethupathib]

Overview

This repository is a study collection of standalone C/C++ algorithm implementations (physical-design / EDA topics: Steiner routing, MST/DSU, LCA variants). It has no build system, package manager, dependency manifest, tests, or lint config — each source file has its own main() and is compiled/run individually with g++.

Changes

• Added AGENTS.md documenting the toolchain, how to compile/run each program, and the file-I/O (freopen) gotcha for lca1, lca_dp, lca_timer, and euler_tours.

Environment

• Update script (startup): g++ --version — a lightweight toolchain sanity check; there are no project dependencies to install (g++/gcc/make/clang++ are preinstalled).

Verification

All programs compile and run cleanly:

• dsu.cpp, kruskals_mst.cpp, lca_tarjans/lca.cpp → stdout
• sparse_table.cpp → RMQ over stdin
• lca_dp/lca_dp.cpp → binary-lifting LCA via file I/O

build_run_demo.log

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