refactor(workspace): move the workspace packages into internal/workspace

[devin-ai-integration]

What and why

Eighth step of the layer-directory move, on top of the internal/doc pull request. Moves the workspace packages into internal/workspace/:

internal/core/{model,libs (with errata),project,envvar} → internal/workspace/{model,libs,project,envvar}

A mechanical relocation: git mv, import-path rewrite across the root module and tools/ (tools/gen/snapshot, tools/census/grammar), the layering-test keys and tolerated rows, Makefile's LIBS_DIR, scripts/pgo-profile.sh, the path comments in the corpus download scripts, the self-model's goPackage references, and link-only path fixes in README.md and docs/internals/architecture.md that the link checker required. internal/workspace/libs/testdata/training_examples_expected.txt moves unchanged.

Two baseline lines move for path reasons:

• the examples digest in docs/project/pilot-differential-baseline.json, because the self-model's goPackage strings changed;
• the provenance.errataRegistry digest (and the errata entries' path strings) in docs/project/pilot-differential-baseline.json, docs/project/pilot-rejection-baseline.json and docs/project/pilot-xpect-baseline.json, because it hashes the errata entries' paths, which embed libs/errata's LibraryRoot constant — now internal/workspace/libs/stdlib. Re-recorded with pilot-diff -update, pilot-reject -update and pilot-xpect -update; the bucket counts are identical to the committed ones (pilot-xpect: 1296 agree / 30 disagree).

How it was verified

go build ./..., go vet ./..., gofmt -l . (empty), make lint, make docs-check, the full suite with OPENSYSML_REQUIRE_TRAINING_CORPUS=1 OPENSYSML_REQUIRE_PILOT_CORPORA=1 OPENSYSML_REQUIRE_PILOT_LIBRARY_XMI=1 go test -count=1 ./... (79 packages ok, none failing), the tools/ module (build, vet, test; doc-counts -check), python3 scripts/changelog.py check. go list ./internal/... | wc -l (59) is unchanged.

Checklist

• make test and make lint pass locally
• Tests added or updated for the change
• Documentation extended where it already covers the surface (see CONTRIBUTING.md)
• Changelog entry added as changes/unreleased/<slug>.<section>.md, not as an edit to CHANGELOG.md
• baselines regenerated and make docs-counts run if a gate count moved (compliance rows need nothing: the census is counted at docs build)
• No internal work-item labels (waves, slices, F4, K5) in the body, docs, or changelog

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[devin-ai-integration]

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