feat(api): export the Door A public surface; complete the §11 seam table

TDD step 9: package-root exports (materialize_bundle, IngestResult, the
typed error hierarchy, manifest types) and the two missing named seam
tests — provenance stamping verified with an independent frontmatter
parser, and navigability verified by resolving every index link. The
test module header maps all six library-side §11 seams to their named
tests; spec integrity stays with commons.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QeqhJpYQyghASjiJo5EhGg

src/llm_ingestion_okf/__init__.py

@@ -5,8 +5,43 @@ deterministic materialization -> index), a bundle inbox converting common
 file types to OKF concepts, and import of external OKF bundles. Security is
 delegated to llm-ingestion-guard at every persist gate.
 
-Pre-implementation: no pipeline code yet. See README.md and CLAUDE.md for
-scope and boundaries.
+Door A (spec-based ingestion) public surface: materialize_bundle plus the
+typed error hierarchy rooted in IngestError.
 """
 
+from .errors import (
+    IngestError,
+    ManifestError,
+    MaterializationError,
+    NetworkGateError,
+    RenderError,
+    SourceError,
+)
+from .manifest import (
+    Extraction,
+    FileSource,
+    HttpSource,
+    Manifest,
+    SqlSource,
+    load_manifest,
+)
+from .materialize import IngestResult, materialize_bundle
+
 __version__ = "0.1.0"
+
+__all__ = [
+    "Extraction",
+    "FileSource",
+    "HttpSource",
+    "IngestError",
+    "IngestResult",
+    "Manifest",
+    "ManifestError",
+    "MaterializationError",
+    "NetworkGateError",
+    "RenderError",
+    "SourceError",
+    "SqlSource",
+    "load_manifest",
+    "materialize_bundle",
+]