docs(lt-dev): replace the unpassable check:envs acceptance with the env contract test

[DKoenig9]

Why

fullstack-updater and modernizing-toolchain required <pm> run check:envs to print "All env configurations OK." as a done signal. That could never happen: scripts/check-envs.sh in nest-server-starter was broken on every machine.

Measured in nest-server-starter at c3912e8:

• scripts/check-envs.sh:137 waited for Server startet at, but src/main.ts:140 logs Server started at (the typo came in with 00bf0d8). All nine boot cases hit the 60s timeout.
• scripts/check-envs.sh:16 copied tests/fixtures/.env.deployed-test, which .gitignore:82 (.env.*) kept out of every clone, so Phase 2 aborted under set -e.
• Neither scripts/check.mjs nor .github/workflows/test.yml runs check:envs, so nothing ever caught this.

nest-server-starter #57 (merged as e66263c) removed the script and moved the check into src/config.env.spec.ts, so it now runs in every pnpm test.

What changes

• Acceptance (fullstack-updater success criteria, modernizing-toolchain done signals): src/config.env.spec.ts covers every entry of REQUIRED_DEPLOYED_ENV_VARS and passes in <pm> test.
• Migration checklist Phase 8 now describes that contract test instead of check-envs.sh plus a fixture. It keeps a dated incident note so the script does not get reintroduced.
• check:envs entries are removed from the Phase 5 script blocks. The check:envs job is removed from the Phase 10 GitLab CI recipe, and check-envs.sh is removed from the upstream file list in checking-upstream-first.

Checked

• claude plugin validate plugins/lt-dev passes, scripts/scan-secrets.sh is clean, and check-cross-references.ts reports 0 broken references.
• Swept every run <script> name and every scripts/* path in plugins/lt-dev against the local clones of both starters, lt-monorepo and the CLI. No other dead targets turned up.

Not checked / not changed

• The sweep only covers references that name a script or a CI job. Criteria written as plain prose were not audited.
• The Phase 5 check chain in the migration checklist still shows the old inline chain, while the starter now uses node scripts/check.mjs. That is drift, not an unpassable criterion, so it is left for a separate change.
• No version bump. The release is up to the maintainer.

🤖 Generated with Claude Code