Upgrade Development Status classifier from Alpha to Beta

[codeforester]

Problem

pyproject.toml currently declares:

"Development Status :: 3 - Alpha",

This is inaccurate and actively hurts PyPI adoption. A project at "Alpha" signals to potential consumers that APIs are unstable, the package may break without warning, and production use is discouraged. base-cli no longer matches that description.

Evidence of Beta-level maturity

The package already has:

• A formal API stability policy (docs/api-stability.md) with a documented deprecation process and removal timeline
• A @deprecated decorator and BaseCliDeprecationWarning for managed deprecation
• A published CHANGELOG.md following Keep a Changelog conventions
• Compatibility consumers (compatibility/consumers/) exercised in CI
• Smoke tests across CPython 3.10–3.14 on Linux, macOS, and Windows
• A contract test suite (test_api_stability.py, test_public_api.py, test_json_contracts.py)
• OIDC-based trusted publishing to PyPI with TestPyPI rehearsal support
• A versioned JSON output contract (json-contracts.md) and command protocol (command_protocol.py)
• An adopter readiness guide (docs/adopter-readiness.md) aimed at production teams
• Security documentation including a threat model and security review

Proposed fix

Change pyproject.toml:

# before
"Development Status :: 3 - Alpha",

# after
"Development Status :: 4 - Beta",

This should happen before or alongside the 1.0 readiness work. "Beta" accurately conveys "APIs are stabilizing, production pilots are encouraged, breaking changes are announced." The 5 - Production/Stable classifier should be reserved for the 1.0 release.