fix: clean up CLI notice, unused dotenv dependency, and version checks

[zacman-99]

Summary

Three small, zero-behavioral-risk fixes from a code-review pass:

1. fix(cli): restore coherent twitter verification notice (agent_reach/cli.py)
   The message printed after configure twitter-cookies was a garbled splice of two
   unrelated sentences. Restored one coherent notice grounded in the existing wording used
   by channels/twitter.py and docs/guides/setup-twitter.md. No runtime behavior
   changed beyond correcting the malformed notice.

2. chore(deps): drop unused python-dotenv pin (pyproject.toml, constraints.txt)
   python-dotenv was never imported anywhere in the package or tests, and no code loads
   .env files (env fallback reads live os.environ directly). Removed from both
   dependency locations: the pyproject.toml runtime dependency list and the
   constraints.txt tested-set pin.

3. test: add version-consistency check (tests/test_version_consistency.py, new)
   Enforces the project convention that the version matches across pyproject.toml,
   agent_reach/__init__.py, and the version literals referenced by tests/test_cli.py.
   Uses stdlib regex parsing only (no tomllib) to stay compatible with Python 3.10.

Test results

• pytest tests/test_cli.py tests/test_version_consistency.py → 28 passed
• ruff check agent_reach/cli.py pyproject.toml constraints.txt tests/test_version_consistency.py → clean

Branch and commits

Branch: fix/section-7-cleanup

3bbb2e6 test: add version-consistency check across pyproject, package, cli tests
5b336f5 chore(deps): drop unused python-dotenv pin
c6b5103 fix(cli): restore coherent twitter verification notice

Residual risks

• The new consistency test requires future version bumps to also update the version
  literals in tests/test_cli.py (the failure message spells this out).
• Removing the python-dotenv constraint means fresh environments resolve it only if some
  other dependency requires it; nothing in this repo does. No installed code changes.