feat(governance): 'contextos gate' CLI command and PR Quality Gate Action

[kok-o]

Problem Statement

As outlined in \ENTERPRISE_ROADMAP.md\ (Phase 1), teams adopting AI coding assistants need automated guardrails in CI/CD to prevent 'toxic AI code' from entering main branches (e.g. unverified placeholders // TODO: implement later, undeclared architectural drift, and missing test proofs).

While .github/actions/contextos-gate/action.yml\ exists, it is an internal composite action and lacks a standalone CLI command or diff-level AST / placeholder inspections.

Objective

Create a first-class \contextos gate\ command and modernize the GitHub Action to evaluate Pull Requests and enforce engineering policies before merging.

Scope of Work

1. **CLI Command \contextos gate**:
   • Scan git diff for prohibited lazy patterns (// TODO: implement, // ... rest of code ...).
   • Verify adapter drift (
     ode .agents/ctx.js export all --check).
   • Run skill integrity and schema validation (
     ode .agents/ctx.js validate).
   • Scan for leaked credentials or secrets (\scripts/check-secrets.js).
   • Run project test suites.
2. GitHub Action Integration:
   • Provide a GitHub Action step summary and PR annotation with pass/fail breakdown for each governance check.
   • Support configuration flags (--strict, --allow-todos, --skip-tests).

Acceptance Criteria

• 
  px contextos gate\ runs locally and returns non-zero exit code if prohibited patterns or drift are detected.
• GitHub Action produces a formatted PR Quality Summary in Actions step summary.
• Comprehensive unit tests for \gate\ command under \ ests/gate.test.js.

[kok-o]

Implemented and verified:

• Standalone contextos gate CLI command executes validation, integrity checks, and adapter drift detection without disk mutation (bin/commands.js, tests/consumer-gate.test.js).
• Standalone contextos scan command scans git diff / staged index for prohibited lazy placeholder stubs (// TODO: implement, etc.), secret leaks, and write-scope containment (tests/scan.test.js).
• GitHub Action .github/actions/contextos-gate/action.yml is active with step summaries and annotation support.