chore: add Cloud Agent development environment config

[study8677]

What this changes

Adds a repository-managed Cloud Agent development environment at .cursor/environment.json.

rename is a zero-runtime-dependency, stdlib-only Python 3.11+ CLI. The only setup needed for development is installing the editable package with its dev extras (pytest + ruff). The config therefore uses Cursor's default base image (which already ships Python 3.12 and pip) and a single idempotent install step:

{
  "name": "rename",
  "install": "pip install -e \".[dev]\""
}

No start or terminals are needed — rename is a CLI with no long-running dev server.

Validation

All checks were run on the Cloud Agent VM against this branch:

• pip install -e ".[dev]" — succeeds, and is idempotent (ran twice cleanly)
• ruff check src tests — all checks passed (matches CI)
• pytest -q — 78 passed (matches CI)
• End-to-end: created a synthetic Claude Code session and ran rename list / rename once / rename search; the tool discovered the session, previewed the stale-vs-new title, applied the rename (append-only ai-title line), and re-running was a correct no-op.

The console script rename (and pytest/ruff) install to ~/.local/bin, which login shells already put on PATH via ~/.profile, so they are directly runnable in agent terminals.

Checklist

• pytest passes
• New behaviour is covered by a test (synthetic fixtures only) — n/a, tooling/config only
• No real session data in code, tests, docs, or examples
• Adapters only change titles — never edit/delete/reorder conversations