Remove every GitHub Actions workflow from the fork

[shishiv]

Summary

Removes every GitHub Actions workflow from the fork, so no pull request or main push runs Actions and no required check can hold a merge:

• .github/workflows/ci.yml (lint, portable/serial/Herdr test lanes, macOS Bash, repo invariants)
• .github/workflows/no-mistakes-required.yml (the PR must be raised via no-mistakes compliance check)
• .github/workflows/windows-herdr-spike.yml (manual-dispatch spike)

To keep the local gates working without those files:

• bin/fm-lint.sh skips workflow lint and prints a note when the checkout has no .github/workflows directory. If the directory exists but holds no workflow files, lint still fails, so an accidentally emptied directory is still caught.
• .no-mistakes.yaml declares no_ci: true. no-mistakes reads that setting only from main, so it takes effect once this PR merges. After that, a pipeline run treats a PR with zero checks as ready instead of waiting forever for checks that can't appear. It never waives a check that does register.

Deletes the tests whose only subject was a deleted workflow: tests/fm-ci-workflow.test.sh, tests/fm-no-mistakes-required.test.sh, the Herdr CI step-timeout case in tests/fm-test-run.test.sh, and the current-workflows parse case in tests/fm-lint-workflows.test.sh. Also drops their entries from bin/fm-test-run.sh.

Corrects the docs that linked to or described the deleted CI: CONTRIBUTING.md (the compliance-check paragraph and the required-checks section are replaced by a short "GitHub Actions on this fork" section), docs/configuration.md gate defaults, docs/fm-test-portable-shards.md, docs/verification/public-followup.md, and the operational-home-layout skill.

Consequences to know before merging

• Nothing runs broad regression before a merge any more. Lint, the coverage guard, and the test lanes run only when someone runs bin/fm-lint.sh and bin/fm-test-run.sh locally.
• The deleted repo-invariants job was the only check that rejected tracked data/, state/, config/, projects/, and .no-mistakes/ paths, and that CLAUDE.md and .claude/skills stay pointers. After this PR, only .gitignore guards those paths. If that check should stay, the smallest move is a follow-up that puts it in bin/fm-lint.sh.
• This file set now diverges from upstream kunchenguid/firstmate. Later syncs from upstream will bring the workflows back as conflicts.
• About 60 generic mentions of "CI" remain in docs and skills: the no-mistakes CI step, the upstream shard evidence, and Herdr lane notes. They weren't swept because they describe upstream behavior or the pipeline's own step, not files this fork links to.

Tests

• bin/fm-lint.sh (changed-file mode) passes and prints the new skip note. bin/fm-lint.sh <changed scripts> passes with full analysis.
• tests/fm-lint.test.sh passes, including the new test_default_path_skips_workflow_lint_only_without_a_workflows_dir. That test covers both cases: with no directory, lint exits 0 with the note; with an empty directory, it fails with no GitHub workflow files found.
• tests/fm-lint-workflows.test.sh passes (15 cases).
• bin/fm-doc-audience-check.sh: ok surfaces=119 local_links=694.
• LC_ALL=C bin/fm-test-run.sh --check-coverage: FM_TEST_COVERAGE ok total=241.
• tests/fm-test-run.test.sh: all 38 remaining cases pass except test_jobs_admits_a_concurrent_safe_family. That case fails the same way on unmodified main on this machine: fm-session-lock-ancestry.test.sh reports that the pty-host was not reparented to init. Under the en_US.UTF-8 locale, --check-coverage also fails on unmodified main with comm: input is not in sorted order. Both failures come from the environment, not from this change.

Delivered without the no-mistakes pipeline, as asked.