feat: add zero-config local proof check

[hippoley]

Goal

Make CounterProof produce useful local evidence before a developer has to open a pull request.

New first-run command

counterproof check

It automatically resolves a base branch, detects or accepts the test runner, runs Regression Witness on HEAD vs BASE, runs Proof Integrity, and prints one scoped local evidence result.

Example:

CounterProof local check

Regression       WITNESSED
Evidence scope   SUBMITTED JUDGE
Proof integrity  CLEAN
Strict gate      PASS
Product oracle   UNVERIFIED

Base             main
Runner           pytest
Evidence mode    PRECISE

The wording is deliberate: a red→green witness plus a clean evidence surface is not called VERIFIED, proof ready, product correctness, or merge readiness.

Strict mode

counterproof check --strict

returns non-zero unless both narrow conditions hold:

• exact changed-test evidence is WITNESSED;
• Proof Integrity is CLEAN.

This is a CI-friendly evidence gate, not an approval verdict.

Conservative auto-detection

Base preference:

explicit --base
origin/HEAD
origin/main
origin/master
main
master

CounterProof uses the merge-base with HEAD and refuses to invent a base when none can be resolved. Runner detection reuses the existing onboarding detector; teams can still pass --test-command explicitly.

Real verification

Tests construct a real Git repository, create a feature branch with an actual regression test, run real pytest execution, and perform the detached BASE replay. Clean-install CI also installs the wheel into a fresh environment and executes:

counterproof check --strict

Machine-readable boundary

JSON output keeps the same semantics:

• status: the evidence status, e.g. witnessed;
• strict_gate.passed: only the exact-witness + clean-integrity gate;
• evidence_scope: submitted-judge;
• oracle_alignment: unverified.

Capability truth

counterproof audit and the public capability JSON list local-check as TESTED only after the real-repository and clean-install paths pass.

Why this matters

Before:

install
→ understand --base
→ understand {tests}
→ determine runner
→ run witness
→ run integrity
→ interpret two results

After:

install
→ counterproof check
→ inspect scoped evidence

This PR changes time-to-first-value without expanding what CounterProof claims the evidence proves.