Document install step; add ISSUE_TEMPLATE to doc sources table

[dmccoystephenson]

Summary

Must-fix (from the public-readiness review):

• Adds an "Installation" section to README.md explaining how to register create-dev-loop.md itself as a slash command (symlink into ~/.claude/commands/) — previously the README described what /create-dev-loop does but never said how a first-time visitor gets it registered. Closes README never documents how to install create-dev-loop.md itself as a slash command #96.
• Adds a .github/ISSUE_TEMPLATE/*.md row to CLAUDE.md's "Documentation sources of truth" table — the three issue templates restate the same conventions PULL_REQUEST_TEMPLATE.md already has a row for, and can drift the same way. Closes CLAUDE.md's documentation sources-of-truth table omits .github/ISSUE_TEMPLATE/*.md #81.

Nice-to-have, folded in:

• tests/test_check_docs.py — fixture-based unit tests for check_docs.py's three checks (placeholder sync, README/Steps sync, local-link resolution), wired into CI, so a silently-broken check doesn't read as "0 errors → pass". Closes scripts/check_docs.py has no test coverage of its own #97.
• create-dev-loop.md — adds a "Steps at a glance" anchor-link TOC; Step 3 and Step 4 sit ~450 lines apart with a lot of example content between. Closes create-dev-loop.md has no way to jump to a specific Step #99.
• .github/workflows/ci.yml — pins actions/checkout and actions/setup-python to commit SHAs instead of major-version tags. Closes CI actions pinned to major version tags, not commit SHAs #100.
• scripts/README.md — one-line pointer to CLAUDE.md/CONTRIBUTING.md. Closes scripts/ has no README; repo has no CHANGELOG #101 (no CHANGELOG added — the issue itself says that's fine to skip pre-1.0).

Not included: #98 (delete 13 stale, already-squash-merged branches) — confirmed all 11 currently-stale branches (2 named in the original issue are already gone) are MERGED via gh pr list, but the branch-deletion push was blocked by this environment's auto-mode classifier as a destructive/shared-repo action. Left for the maintainer to run directly:

git push origin --delete feature/add-research-md feature/localization-and-command-sub-fixes feature/rubric-based-self-review fix/doc-accuracy-sweep fix/gh-pr-create-restricted-fetch-refspec fix/no-build-system-guidance fix/research-md-pr54-implementations fix/sandbox-blocks-directory-creation fix/scratch-dir-and-revert-checkpoint fix/step1-update-scratch-file license-mit

Doc sync check

• README.md's "What it does" Step list still matches create-dev-loop.md's Steps 1:1 (unchanged — Installation and the new TOC are outside the Step list)
• Every {{placeholder}} added or changed has a corresponding Step 4 substitution-table row — n/a, no placeholders touched
• RESEARCH.md updated — n/a, no template/phase behavior change

Test plan

• python3 scripts/check_docs.py passes.
• python3 -m unittest discover -s tests -v — 13/13 new tests pass.
• Manually verified the symlink command in the Installation section matches the actual convention already in use (~/.claude/commands/create-dev-loop.md -> .../create-dev-loop.md) and how Step 5 registers generated skills.
• Verified the pinned action SHAs (actions/checkout@11d5960a... = v4.4.0, actions/setup-python@a26af69b... = v5.6.0) resolve to the tagged commits via gh api.
• Verified all 11 branches proposed for deletion show MERGED via gh pr list --state all --head <branch>.

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