docs: create AGENTS.md with CI-enforced rules for coding agents

[sergio-sisternes-epam]

Summary

Creates AGENTS.md at the repository root -- the single authoritative entry point for AI coding agents working in this repository.

Closes #695

What this file provides

A concise, machine-scannable contract covering every CI-enforced rule that agents could violate:

Section	What it covers
Setup	Exact uv sync and verification commands
Before Every Commit	5-step checklist with copy-pasteable lint commands
Code Conventions	YAML I/O rule, path portability, path security, console output, ASCII encoding
CLI Conventions	Help text standards, docs sync requirement
Testing Conventions	Directory structure, mock rules, CI command
Security	CodeQL, secrets policy, path traversal guards
PR Hygiene	Branch naming, CHANGELOG, test script policy
Per-Module Rules	Pointer table to all 6 .github/instructions/*.instructions.md files

Design decisions

1. Top-level entry point, not a duplicate -- AGENTS.md contains directives and points to .github/instructions/ for detailed per-module rules. No content duplication.

2. ASCII-only -- the entire file stays within printable ASCII (U+0020-U+007E), consistent with the encoding rules it documents.

3. 103 lines -- concise and scannable. Agents get rules, not rationale.

4. CLI docs path corrected -- issue [FEATURE] Create root AGENTS.md documenting all CI-enforced rules for coding agents #695 referenced docs/cli-reference.md which doesn't exist. Used the actual path: docs/src/content/docs/reference/cli-commands.md.

5. .gitignore updated -- AGENTS.md was in .gitignore (local development section). Added !/AGENTS.md negation to track the root file while keeping subdirectory AGENTS.md files ignored.

Changes

File	Change
AGENTS.md	New file (103 lines)
.gitignore	Added !/AGENTS.md negation pattern
CHANGELOG.md	Added entry under [Unreleased] > Added

Validation

• All referenced paths in AGENTS.md exist in the repository
• File is ASCII-only (verified with grep -Pn '[^\x09\x0a\x0d\x20-\x7e]')
• All 3,790 unit tests pass (uv run pytest tests/unit tests/test_console.py -n auto --dist worksteal)
• CHANGELOG entry follows Keep a Changelog format

[Copilot]

Pull request overview

Adds a repository-root AGENTS.md intended to be the authoritative, agent-readable checklist of CI-enforced rules and conventions for working in this codebase (closing #695), and ensures it is tracked and documented.

Changes:

• Add new AGENTS.md with setup steps, pre-commit checklist, and pointers to .github/instructions/*.
• Update .gitignore to unignore /AGENTS.md while keeping other AGENTS.md files ignored.
• Add a changelog entry under ## [Unreleased].

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 6 comments.

File	Description
AGENTS.md	New agent contract/checklist and pointers to detailed instruction files.
.gitignore	Ensures the root AGENTS.md is tracked despite a broader ignore pattern.
CHANGELOG.md	Records the addition of AGENTS.md under Unreleased/Added.