Add hub-core package, docs, and State Hub integration scaffold

Extract the first reusable slice (models, schemas, routers, MCP, migrations)
from state-hub with INTENT/SCOPE, agent instructions, workplan, and aligned
inter_hub capability registry index.

hub_core/schemas/doi.py

@@ -0,0 +1,29 @@
+from pydantic import BaseModel
+
+
+class DoICriterion(BaseModel):
+    id: str
+    label: str
+    tier: str
+    status: str
+    detail: str = ""
+
+
+class DoIReport(BaseModel):
+    repo_slug: str
+    tier: str
+    core_pass: bool
+    standard_pass: bool
+    full_pass: bool
+    criteria: list[DoICriterion] = []
+    checked_at: str
+
+
+class DoISummaryEntry(BaseModel):
+    repo_slug: str
+    domain_slug: str | None
+    tier: str
+    core_pass: bool
+    standard_pass: bool
+    full_pass: bool
+    checked_at: str