docs: align Arbiter install package name

[hummbl-dev]

Summary

• update README PyPI badge and install commands to use the pyproject distribution name arbiter-score
• document that arbiter is the installed CLI command, not the package to install
• keep docs/REPO_HEALTH.md aligned with the package identity

Validation

• git diff --check
• stale README/docs package-reference scan returned no matches
• python3 -m pip index versions arbiter-score currently reports no matching distribution; python3 -m pip index versions arbiter reports a separate public distribution, so this PR avoids that ambiguity

Closes #71

[hummbl-dev]

Post-merge Codex peer review of 0f905d6b267afe99f67fef760ea33287ee5fb39e.

Verdict: FOLLOW-UP NEEDED (P2 docs/install accuracy).

Finding: README now makes the primary install path a package that is not currently published.

README.md:15-27 presents pip install arbiter-score and pip install "arbiter-score[analyzers]" as the main install commands. I verified the current package index from the review worktree:

python -m pip index versions arbiter-score
ERROR: No matching distribution found for arbiter-score

python -m pip index versions arbiter
arbiter (1.1.2)
Available versions: 1.1.2, 1.1.1, 1.1.0, 1.0.1, 1.0.0

The PR correctly avoids pointing users at the separate public arbiter project, and it matches pyproject.toml (name = "arbiter-score", CLI script arbiter). But until arbiter-score is actually published, the public README install section is still broken for users: the first command fails.

Recommended fix-up: keep the package identity note, but make source install the current primary path and label PyPI install as pending publication, or publish arbiter-score before treating pip install arbiter-score as current install guidance. docs/REPO_HEALTH.md:14 already says "PyPI-oriented package", and docs/REPO_HEALTH.md:62 references publish verification before PyPI publish, so this can be framed cleanly without reintroducing the wrong arbiter package.

Validation:

• git diff --check HEAD^..HEAD passed.
• Hosted CI for merge commit 0f905d6b267afe99f67fef760ea33287ee5fb39e succeeded: https://github.com/hummbl-dev/arbiter/actions/runs/25867161761