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>

src/infospace_bench/__init__.py

@@ -1,3 +1,4 @@
+from .archive import ArchiveRecord, archive_infospace, list_archives
 from .errors import InfospaceError
 from .evaluation import EntityEvaluation, EvaluationSnapshot, MetricValue, ScoreEntry
 from .engine import (
@@ -40,6 +41,7 @@ from .semantics import EntityRecord, RelationRecord, list_entities, list_relatio
 from .workflow import load_workflows, plan_workflow, run_workflow
 
 __all__ = [
+    "ArchiveRecord",
     "DisciplineBinding",
     "EntityEvaluation",
     "EvaluationSnapshot",
@@ -60,11 +62,13 @@ __all__ = [
     "ViabilityThreshold",
     "add_artifact",
     "append_to_history",
+    "archive_infospace",
     "create_infospace",
     "engine_capability_contract",
     "find_snapshot",
     "get_history",
     "get_latest_snapshot",
+    "list_archives",
     "list_entities",
     "list_relations",
     "load_infospace",