feat(twin): require the base-artifact type at the repository's own constructor

[nilsonfh]

Summary

The next phase of bd 6ns.1: NetworkModelRepository.from_parquet now requires BaseArtifactDir.

#54 typed the producer (ArtifactLayout.base), the repository field, the readers and the argparse boundaries, but its own commit message said plainly what it did not cover: from_parquet still accepted any path-like, so from_parquet(script.root) type-checked — at the constructor most callers use, and exactly the swap bd 7rt made. This closes it.

Why it waited

Narrowing alone raised the gridalyn ratchet 116 → 119 when measured during #54, because three workflow functions declared base_dir: Path and passed it straight in. So they come first:

• generate_ev_scenarios, generate_flexibility_provider_artifacts, generate_semantic_graph now take BaseArtifactDir.
• generate_semantic_graph re-wraps after base_dir.resolve(), which returns a plain Path.
• from_parquet's body still passes the value through Path(), so a caller holding a str or a Path keeps working at run time; only what mypy accepts changes.
• All three functions gained the docstring they never had, documenting every parameter, base_dir included — the condition agreed with the twin's owner for anything this work annotates.

Verification

• Simulated first on a throwaway worktree of main, mypy A/B per (file, message): 0 new errors in all three targets. A positive control confirmed a plain Path into from_parquet is now rejected, so mypy was reading the patched tree.
• On this branch: pinned black/isort/flake8 clean; touched modules import at run time; ratchets 116 / 846 / 12, identical to main; 57 targeted tests pass; full suite 2260 passed / 0 failed.

What is still untyped, stated rather than implied

• argparse hands these scripts an Any, so the boundary is held by the type= converters added in feat(foundation): type the canonical base-artifact directory of an instance #54, not by these signatures. Measured on this branch, the value still arrives at from_parquet unchecked at generate_digital_twin_dashboard_catalog.py:104 (args.base_dir) and at tools/r7_twin_consumer_identity.py:167 (tools/ carries no ratchet).
• Tests pass bare Paths at 46 call sites (counted, not estimated). No ratchet type-checks tests, and run time still accepts them, because the body converts.
• So "typed" here means typed where mypy looks. The claim is kept the size of the evidence (raised in review).

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