Add ArtifactStore and extraction layer for in-memory artifact search

Introduces DuckDB-backed store, row extractors for all 4 artifact types
(manifest, catalog, run_results, sources), table DDL definitions, and
error hierarchy for the ARTIFACT_SEARCH toolset (PR 2 of 3).

Author: jairus-m

.changes/unreleased/Under the Hood-20260514-151517.yaml

@@ -0,0 +1,3 @@
+kind: Under the Hood
+body: Add in-memory DuckDB artifact store with extraction layer for structured artifact querying
+time: 2026-05-14T15:15:17.615904-07:00

pyproject.toml

@@ -45,6 +45,7 @@ dependencies = [
   "filelock~=3.20.3",
   "starlette~=0.50.0",
   "dbt-artifacts-parser>=0.13.2",
+  "duckdb>=1.5.2",
 ]
 [tool.uv]
 exclude-newer = "7 days"