feat(state-hub): implement v0.5 — dynamic domains & multi-repo

Replaces the hardcoded 6-domain PostgreSQL ENUM with a first-class
`domains` DB table, and adds a `managed_repos` table for multi-repo
support per domain.

P1 — Domain as a DB entity:
- Migration b1c2d3e4f5a6: creates `domains` table, migrates topics.domain
  ENUM column to domain_id FK, drops the domain ENUM type
- Domain ORM model (api/models/domain.py) + Pydantic schemas
- Domain API router: GET/POST /domains/, GET/PATCH /domains/{slug}/,
  rename and archive endpoints with EP/TD cascade on rename
- Topic model updated: domain_id FK + @property domain_slug for
  backwards-compatible JSON serialization (field renamed domain → domain_slug)
- TopicCreate/TopicRead updated; seed.py rewritten to use FK lookup

P2 — Multi-repo support:
- ManagedRepo ORM model (api/models/managed_repo.py) + schemas
- Repo API router: GET/POST /repos/, GET/PATCH /repos/{slug}/, archive
- Makefile: add-domain, rename-domain, add-repo, list-repos targets
- register_project.sh: verify domain via /domains/ API + POST /repos/

P3 — MCP tools & live validation:
- 6 new MCP tools: list_domains, create_domain, rename_domain,
  archive_domain, list_domain_repos, register_repo
- EP/TD routers: replace hardcoded VALID_DOMAINS set with per-request
  DB lookup — returns 422 with list of valid slugs on unknown domain
- State summary: adds domains: list[DomainSummary] (slug, name,
  repo_count, active_workstream_count, ep_count, td_count)
- TOOLS.md updated with domain management section

P4 — Dashboard:
- New domains.md page with KPI row + domain cards + repo lists
- domains.json.py + repos.json.py data loaders
- Domains page added to observablehq.config.js nav
- workstreams.md, extensions.md, techdept.md: domain_slug fix +
  dynamic domain list loaded from /domains/ API (no longer hardcoded)

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

api/routers/topics.py

@@ -5,12 +5,22 @@ from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from api.database import get_session
+from api.models.domain import Domain
 from api.models.topic import Topic, TopicStatus
 from api.schemas.topic import TopicCreate, TopicRead, TopicUpdate, TopicWithWorkstreams
 
 router = APIRouter(prefix="/topics", tags=["topics"])
 
 
+async def _resolve_domain_id(domain_slug: str, session: AsyncSession) -> uuid.UUID:
+    """Resolve a domain slug to its UUID. Raises 404 if not found."""
+    result = await session.execute(select(Domain).where(Domain.slug == domain_slug))
+    domain = result.scalar_one_or_none()
+    if domain is None:
+        raise HTTPException(status_code=404, detail=f"Domain '{domain_slug}' not found")
+    return domain.id
+
+
 @router.get("/", response_model=list[TopicRead])
 async def list_topics(
     status: TopicStatus | None = None,
@@ -29,7 +39,14 @@ async def create_topic(
     body: TopicCreate,
     session: AsyncSession = Depends(get_session),
 ) -> Topic:
-    topic = Topic(**body.model_dump())
+    domain_id = await _resolve_domain_id(body.domain, session)
+    topic = Topic(
+        slug=body.slug,
+        title=body.title,
+        description=body.description,
+        domain_id=domain_id,
+        status=body.status,
+    )
     session.add(topic)
     await session.commit()
     await session.refresh(topic)
@@ -56,7 +73,10 @@ async def update_topic(
     topic = await session.get(Topic, topic_id)
     if topic is None:
         raise HTTPException(status_code=404, detail="Topic not found")
-    for field, value in body.model_dump(exclude_unset=True).items():
+    updates = body.model_dump(exclude_unset=True)
+    if "domain" in updates:
+        topic.domain_id = await _resolve_domain_id(updates.pop("domain"), session)
+    for field, value in updates.items():
         setattr(topic, field, value)
     await session.commit()
     await session.refresh(topic)