docs: remove internal engineering docs; docs must be tool- or story-relevant

Operator policy: docs in the public repo must help (a) a user
deploying certctl or (b) the product story. Internal engineering
process documentation belongs in cowork/ scratchpads or in git
commit history, not docs/.

Removed (docs/contributor/, 8 files, 2,323 lines):
  - release-sign-off.md         — internal release-day checklist
  - ci-pipeline.md              — what runs in CI (internal)
  - ci-guards.md                — what the guards are (internal)
  - testing-strategy.md         — internal testing strategy
  - qa-test-suite.md            — internal QA reference (445 lines)
  - qa-prerequisites.md         — internal QA setup
  - gui-qa-checklist.md         — manual GUI QA checklist
  - test-environment.md         — 1,103-line redundant with
                                  docs/getting-started/quickstart.md +
                                  docs/getting-started/advanced-demo.md

Removed supporting script:
  - scripts/qa-doc-seed-count.sh — CI guard for the deleted
                                   qa-test-suite.md seed-data table

Cross-reference cleanup:
  - README.md: dropped the Contributor audience row + footer
    pointer to docs/contributor/.
  - Makefile: dropped `verify-docs` target + qa-stats comment refs.
  - .github/workflows/ci.yml: dropped the QA-doc seed-count drift
    CI step + dead comment refs.
  - docs/reference/cli.md: repointed qa-prerequisites.md → quickstart.md.
  - docs/operator/performance-baselines.md: dropped ci-pipeline.md
    cross-ref.
  - scripts/ci-guards/README.md: dropped the 'Guards explicitly
    NOT here' section that referenced the deleted QA-doc guards.

G-3 env-docs-drift guard improvements (a real consequence: deleting
the contributor docs surfaced that some env vars only had a home
there). Refit the guard to the new doc topology:
  - Defined-scan widened from `config.go + cmd/*` to all of `cmd/ +
    internal/` (production code), excluding `*_test.go` — catches
    service-layer env vars like CERTCTL_STEPCA_ROOT_CERT and
    CERTCTL_ZEROSSL_EAB_URL that were previously invisible to the
    guard.
  - Docs-scan widened to include deploy/ENVIRONMENTS.md (the
    canonical env-var inventory table — should have been in scope
    from day one). Kept narrow to README + docs/ + deploy/helm/ +
    ENVIRONMENTS.md to avoid pulling in compose/test fixtures.
  - ALLOWED filter now applies to both DOCS_ONLY and CONFIG_ONLY
    directions, so dynamic per-profile dispatch surfaces
    (CERTCTL_SCEP_PROFILE_<NAME>_*, CERTCTL_EST_PROFILE_<NAME>_*,
    CERTCTL_QA_*) don't need static doc entries.
  - Added CERTCTL_SCEP_PROFILE_[A-Z_]+ and CERTCTL_EST_PROFILE_[A-Z_]+
    to ALLOWED for the same reason.

deploy/ENVIRONMENTS.md: added CERTCTL_ZEROSSL_EAB_URL row — real
operator override (overrides the ZeroSSL EAB-credentials endpoint;
read at internal/connector/issuer/acme/acme.go:372) that was
defined in Go source but never documented. G-3 caught it after the
defined-scan widened.

scripts/ci-guards/S-1-hardcoded-source-counts.sh: removed dead
WORKSPACE-CHANGELOG.md allowlist entry (the file was deleted in
the prior workspace cleanup).

Verified:
  All 35 scripts/ci-guards/*.sh green (FAIL=0).
  No remaining references to docs/contributor/ or qa-doc-seed-count
  in tracked files.

scripts/ci-guards/README.md

@@ -41,8 +41,6 @@ Current helpers:
   `PR_NUMBER` + `GH_TOKEN` env from the go-build-and-test job
 - `scripts/check-coverage-thresholds.sh` — consumes `coverage.out`
   + `.github/coverage-thresholds.yml`
-- `scripts/qa-doc-part-count.sh` + `scripts/qa-doc-seed-count.sh` —
-  invoked via `make verify-docs` pre-tag, not in CI
 
 ## Adding a new guard
 
@@ -97,12 +95,6 @@ The cold-DB compose smoke (post-v2.1.0 / item-6) is NOT a script in this directo
 
 The fourth Bundle artifact (`internal/ciparity/`) is Go tests, not shell guards — runs under the standard Go test step. Pins the MCP tool catalogue floor + naming convention; reports CLI/MCP/OpenAPI surface counts as a trend metric.
 
-## Guards explicitly NOT here
-
-- **`QA-doc Part-count drift`** + **`QA-doc seed-count drift`** — these
-  protect docs-the-operator-reads, not anything the product depends on.
-  Moved to `make verify-docs` (operator runs pre-tag, not on every push).
-  See the ci-pipeline-cleanup spec, Phase 11.
 
 ## Running the full set locally