docs(test): document local harness and act usage

[Omegaice]

Documents how to run the test harness and the CI workflow locally without the spurious failures a template-development checkout produces, and adds the guidance as a dev-only Claude rule.

What

• scripts/test/README.md: a Python-dependencies subsection (the kg-frontmatter-graph test asserts yaml/rdflib/pyshacl rather than skipping), a warning against pointing MVP_TEMPLATE_LOCAL at a working tree containing gitignored artifacts, and a "Running the CI workflow locally with act" section.
• .claude/rules/local-testing.md: the same guidance in agent-facing form for template contributors.
• scripts/instantiate.sh: the new rule joins observe-the-failure.md in DEV_ONLY_RULES so it never ships to derived projects.
• instantiate-strips-dev-rules smoke test: precondition + strip assertions for the new rule.

Why

Three local failure modes motivated this, all invisible in CI's clean checkouts:

1. MVP_TEMPLATE_LOCAL at a dev checkout copies the dogfooded wiki/<template>.wiki/ into the sandbox via cp -R, and init-wiki.sh fails with "multiple wikis ... name is ambiguous".
2. The kg test's Python deps are asserted, so a bare local run fails 6 assertions.
3. act --bind writes root-owned scripts/kg/build/ and scripts/kg/.cache/ into the host checkout (the kg pipeline writes into the repo, not the test sandbox) and leaks the same gitignored artifacts into the workflow's MVP_TEMPLATE_LOCAL=$GITHUB_WORKSPACE. act's default copy mode avoids both, since --use-gitignore makes the container see the equivalent of a clean checkout.

Verification

• The new strip assertion was observed red before the DEV_ONLY_RULES change (rule shipped and survived instantiation) and green after; a precondition assertion guards against a vacuous pass.
• Full harness on this tree: 991 pass, 0 fail (989 + the 2 new assertions).
• act -j test --matrix os:ubuntu-latest --rm runs the workflow's ubuntu leg green with no writes to the host tree.