ci: workflows install the editable package with --no-build-isolation (Part of #4918)

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Part of #4918 (closes the pip install -e . build-isolation gap listed in #4944).

Workflow editable installs built with isolation fetched an unpinned setuptools/setuptools_scm. Every pip install -e in .github/workflows now passes --no-build-isolation, using the backend from the hash-locked ci/requirements/bootstrap.txt (#5355).

• 29 workflows, 38 one-line changes (the owner patch from the churn handoffs dir, applied unchanged; mechanical, hence the file count).
• tests/core_engine/test_ci_install_pins.py: removed the strict xfail on test_workflows_build_without_isolation; it now enforces the rule.
• tests/tools/test_pr_gates_fleet.py: the mypy-audit assertion still named the removed tests/requirements-mypy.txt (stale since ci: hash-lock the mypy toolchain; local installs use the locked backend (Part of #4918) #5355); now names ci/requirements/mypy.txt.

Needs owner review: workflow files are CODEOWNERS-protected. A job that lacks the bootstrap lock install before the editable install would fail; the gate test checks every workflow for this.

Class table

Member	Status
workflow pip install -e (all variants: ., ./gitgalaxy, ./main, extras)	fixed here
publish.yml python -m build (isolated)	sibling gap
workflow pip install -r requirements.txt (smoke-test, full-suite-gate, os-smoke-grid), unhashed	sibling gap
tests/tools venv scripts (crucible_check) local pip install -e	local tooling

No burned mainframe estate needs any of these. No golden bless (no parsing change).

Gates: pr_gates --fast 6/6, --ratchets 8/8, audit_check.py clear, tests/tools 1358 pass. One failure not caused by this change: test_pin_requirements_check_all reports ci/requirements/pytest.txt and test.txt STALE (lockfiles untouched here; likely the local pip-compile environment, not re-checked on main).

Cross-repo: none.

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Waiting on an owner decision (asked privately, 2026-10-18). Nothing is needed from contributors; work resumes once it is answered.

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