WP-0001-T014: minimal HTTP app and CLI

src/artifactstore/app.py (new): composition root. build_registry(settings)
wires AsyncEngine + LocalBackend + InProcessDataPlane + RegistryViewWriter
into a Registry. Used by both the HTTP app and the CLI.

src/artifactstore/registry/__init__.py: adds db_health() (SELECT 1 probe),
backend_health() (pass-through to dataplane), and dispose() (engine
shutdown) helpers so the HTTP /health endpoint and CLI commands can talk
to the registry without reaching for private state.

src/artifactstore/api/http/__init__.py:
- create_app(settings=None) factory; lifespan owns the registry instance
  and disposes it on shutdown.
- GET / returns the scaffold banner.
- GET /health reports overall status + db {healthy, detail} + backend
  {backend_id, healthy, detail, free_bytes, total_bytes}. Uses
  FastAPI Depends() with a request->state.registry helper rather than
  reaching app.state directly.
- Module-level `app = create_app()` so `uvicorn artifactstore.api.http:app`
  keeps working.

src/artifactstore/cli/__init__.py:
- migrate: `alembic upgrade head` via the alembic command API.
- replay: drops + rebuilds materialised views from the event log; prints
  the highest applied sequence.
- health: prints the same payload as the HTTP /health endpoint, as JSON.
- version unchanged.

Tests:
- tests/integration/test_http_health.py (TestClient-based): /
  scaffold banner; /health reports ok with db.healthy + backend.healthy
  + free_bytes populated.
- tests/integration/test_cli_commands.py (typer CliRunner): version
  prints; migrate creates the schema (events + retention_classes +
  alembic_version); replay against an empty log exits ok with
  "replayed up to sequence 0"; health prints a status=ok JSON payload.

Gates: ruff clean, mypy --strict clean on 48 files, 83 tests pass.

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

src/artifactstore/registry/__init__.py

@@ -25,7 +25,7 @@ from typing import Any
 from uuid import UUID
 
 import cbor2
-from sqlalchemy import select
+from sqlalchemy import select, text
 from sqlalchemy.ext.asyncio import AsyncEngine
 
 from artifactstore.dataplane.spi import DataPlane
@@ -61,6 +61,7 @@ from artifactstore.manifest import (
 )
 from artifactstore.manifest.codec import decode as manifest_decode
 from artifactstore.manifest.projection import jcs_projection
+from artifactstore.storage.spi import BackendStatus
 
 __all__ = ["Registry"]
 
@@ -316,6 +317,29 @@ class Registry:
             poll_interval_seconds=poll_interval_seconds,
         )
 
+    # ---- health / lifecycle -------------------------------------------------
+
+    async def db_health(self) -> tuple[bool, str]:
+        """Probe the database with ``SELECT 1``.
+
+        Returns ``(healthy, detail)``; ``detail`` is "ok" on success and the
+        exception message on failure.
+        """
+        try:
+            async with self._engine.connect() as conn:
+                await conn.execute(text("SELECT 1"))
+        except Exception as exc:
+            return False, f"{type(exc).__name__}: {exc}"
+        return True, "ok"
+
+    async def backend_health(self) -> BackendStatus:
+        """Probe the configured storage backend through the data plane."""
+        return await self._dataplane.backend_health()
+
+    async def dispose(self) -> None:
+        """Release the engine's connection pool. Idempotent."""
+        await self._engine.dispose()
+
     # ---- internals ----------------------------------------------------------
 
     async def _validate_retention_class(self, retention_class: str) -> None: