docs: add AGENTS.md guidance for AI coding agents

[kikoso]

Overview

Adds an AGENTS.md at the repo root with guidance for AI coding agents working on this repository, following the agents.md convention. Also adds a one line CLAUDE.md pointer so Claude Code picks up the same file.

Content

• Table of the modular layout (library, clustering, heatmaps, data, ui, maps-utils aggregator, lint-checks, demo, visual-testing) with a pointer to MIGRATION.md
• Build, test and lint commands
• API key setup for the demo app
• Code style rules: match the language of the file being edited, .editorconfig formatting, API compatibility expectations, and placing changes in the most specific submodule
• PR conventions, including that release-please parses Conventional Commit prefixes and that CHANGELOG.md and the release manifest are machine generated
• The AI contribution policy from CONTRIBUTING.md

Note: bom/ and collections/ are tracked with build files but are not currently wired into settings.gradle.kts, so they are left out of the module table for now.

This gives contributors using any coding agent one canonical instructions file, in line with the standardization discussion in googlemaps-samples/android-maps3d-samples#62.

[googlemaps-bot]

Code Coverage

Overall Project	50.4%	🍏

There is no coverage information present for the Files changed