feat(gems): three-pass schema migration aligning state-hub with GEMS

Implements CUST-WP-0007. Resolves inconsistencies I-1, I-2, I-5, I-6
identified in the GEMS audit (GenericEntityModellingSystem.md).

Pass 1 (e1f2a3b4c5d6): domain_id FK on extension_points and
technical_debt (replaces raw string column); repo_id FK on contributions.
Fixes domain-filtering bugs in EP/TD dashboard pages.

Pass 2 (f2a3b4c5d6e7): repo_id nullable FK on workstreams, aligning
the GEMS primary attachment with ADR-001 (repo > topic). Dashboard
pages updated to prefer repo->domain over topic->domain.

Pass 3 (a3b4c5d6e7f8): SBOMSnapshot container entity (GEMS Complex
between Repository and SBOMEntry). Ingest is now additive — each call
creates a new snapshot; history is retained. List/report endpoints
filter to latest snapshot per repo via _latest_snapshot_ids_subquery().
New endpoints: GET /sbom/snapshots/, GET /sbom/snapshots/{id}/.
Dashboard gains a Snapshot History section.

Also adds GEMS analysis artefacts: wiki/GEMS-StateHub-TypeRegistry.md,
wiki/GEMS-StateHub-SWOT.md, workplans/CUST-WP-0006 (analysis),
workplans/CUST-WP-0007 (migration, now completed).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcp_server/server.py

@@ -219,6 +219,7 @@ def create_workstream(
     description: str | None = None,
     owner: str | None = None,
     due_date: str | None = None,
+    repo_id: str | None = None,
 ) -> str:
     """Create a new workstream under a topic and emit a progress_event.
 
@@ -229,6 +230,7 @@ def create_workstream(
         description: optional longer description
         owner: optional owner name
         due_date: optional ISO date string (YYYY-MM-DD)
+        repo_id: UUID of the owning repository (GEMS primary; strongly recommended per ADR-001)
     """
     if not slug:
         slug = re.sub(r"[^a-z0-9]+", "-", title.lower()).strip("-")
@@ -240,6 +242,7 @@ def create_workstream(
         "owner": owner,
         "due_date": due_date,
         "status": "active",
+        "repo_id": repo_id,
     })
     _post("/progress", {
         "topic_id": topic_id,
@@ -975,8 +978,8 @@ def get_contributions(
 def ingest_sbom_tool(repo_slug: str, lockfile_path: str) -> str:
     """Ingest a lockfile into the State Hub SBOM store for a repo.
 
-    Parses the lockfile and POSTs entries to /sbom/ingest/. Old entries
-    for the repo are replaced (snapshot strategy).
+    Parses the lockfile and POSTs entries to /sbom/ingest/. Each call creates
+    a new SBOMSnapshot; previous snapshots are retained as history.
 
     Args:
         repo_slug: Managed-repo slug (must be registered via register_repo)