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, plus a one line CLAUDE.md pointer so Claude Code picks up the same file. Companion to googlemaps/android-maps-compose#993 and googlemaps/android-maps-utils#1773.

Content

• Map of the repo areas (ApiDemos, snippets, tutorials, FireMarkers, WearOS)
• A dedicated section on the snippets modules: the [START]/[END] region tags feed the documentation site, so agents must not rename tags or reformat tagged code, and Java/Kotlin snippet modules must stay in sync
• The same parity rule for ApiDemos java-app and kotlin-app
• Build commands including scripts/verify_all.sh, and the API key setup via local.defaults.properties / local.properties
• PR conventions, including that release-please parses Conventional Commit prefixes and CHANGELOG.md is machine generated
• A pointer to the AI-assisted contribution policy already in CONTRIBUTING.md

Samples repos receive a growing share of AI-generated contributions, and the snippets-to-docs pipeline is exactly the kind of non-obvious constraint agents break without written guidance.

[snippet-bot]

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