IB-WP-0014: archive integration with artifact-store (T01+T02)

Reframe IB-WP-0014 from "in-repo S3/git backend adapters" to "durable archive
surface via artifact-store". The live infospace stays in a local working folder;
finalized snapshots are bundled into content-addressed artifact-store packages.

- New module infospace_bench.archive: archive_infospace(), list_archives(),
  ArchiveRecord. Self-bootstraps a SQLite + local-FS registry under
  output/archives/.store/ when no Registry is passed in.
- New output/archives/index.yaml records each archive event (package id,
  manifest digest, retention class, included paths, file count, note).
- artifactstore added as a path dep; Python floor bumped to 3.12 to match.
- Makefile for venv-based dev setup; stack-and-commands.md updated.
- tests/test_archive.py covers index write, list, recursive-capture guard,
  caller-supplied include, and empty-include error. Full suite 65 passed.

Remaining tasks (T03 list CLI, T04 restore, T05 docs) tracked in the workplan.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Makefile

@@ -0,0 +1,29 @@
+PYTHON ?= .venv/bin/python
+UV ?= uv
+
+.PHONY: help venv install test test-archive clean
+
+help:
+	@echo "infospace-bench dev targets"
+	@echo
+	@echo "  make venv          create ./.venv via uv"
+	@echo "  make install       install path deps (markitect-tool, artifactstore) into .venv"
+	@echo "  make test          run the full pytest suite"
+	@echo "  make test-archive  run only the artifact-store archive integration tests"
+	@echo "  make clean         remove ./.venv and pytest caches"
+
+venv:
+	$(UV) venv
+
+install: venv
+	$(UV) pip install -e .
+	$(UV) pip install pytest pytest-asyncio
+
+test:
+	$(PYTHON) -m pytest -q
+
+test-archive:
+	$(PYTHON) -m pytest tests/test_archive.py -q
+
+clean:
+	rm -rf .venv .pytest_cache