ci: add CI, PR template, CODEOWNERS (#5)

[andybaran]

Closes #5.

[andybaran]

🔬 Code review (code-review agent)

Verdict: APPROVED — 0 Critical, 0 Important, 0 Minor.

Verified against Approved Plan v2, executed CI commands on the branch:

• Scope clean & parallel-merge safe: only .github/CODEOWNERS, .github/pull_request_template.md, .github/workflows/ci.yml.
• ShellCheck glob is the corrected post-rename path (skills/issue-driven-github-flow/scripts/*.sh tests/*.sh) — the fix that reversed v1 rejection; both targets exist, shellcheck exit 0.
• Triggers pull_request + push to main; ubuntu-latest; pinned actions/checkout@v4 before shell steps; apt install with sudo ... update && -y.
• Dependency-light: evals lint uses stdlib json only; no PyYAML, no blocking actionlint/yamllint. No swallowed failures (bare commands fail the job).
• PR template checklist + CODEOWNERS * @andybaran valid. No secrets/stray files.

Human orchestrator performing final squash-merge.