docs: add AGENTS.md; bump version to 3.2.1+1

[YASoftwareDev]

Summary

• Adds AGENTS.md with AI assistant context: repo layout, import paths, stub generation, shim package, dependency constraints, CI and commit conventions.
• Bumps version to 3.2.1+1 (post-release tag, docs-only change).
• Updates CHANGELOG with 3.2.1+1 entry.

Replaces #3 (closed — original branch had unresolvable conflicts from stale CI commits already on main).

Test plan

• uv pip install -e . still works
• from tts_service_api import VERSION; print(VERSION.__version__) prints 3.2.1+1