feat(engine): page-store kernel skeleton (WP-0014 T1)

engine/ package: EngineKernel (in-process page store with per-page version
history; create/edit-as-version, recoverable delete-tombstone, keys, current_rev)
+ wikilink extraction + in-shard link resolution / red-link detection (EC-1..EC-4).
Reuses model/provenance; git-IS-store backing slots in later. 6 tests green,
pyflakes clean, full suite green. Marks T1 done.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/shard_wiki/engine/__init__.py

@@ -0,0 +1,11 @@
+"""engine/ — shard-wiki's native, headless wiki engine (a canonical-mode shard backend).
+
+A small page-store kernel + a typed-extension runtime (WikiEngineCoreArchitecture). The engine
+is *one shard*: it is consumed by the orchestrator only via its `EngineShardAdapter`; it never
+imports the derived tier (`union`/`projection`).
+"""
+
+from shard_wiki.engine.kernel import EngineKernel
+from shard_wiki.engine.links import extract_wikilinks
+
+__all__ = ["EngineKernel", "extract_wikilinks"]