refactor(makefile): rename start → backend, add restart logic for api and dashboard

- `make backend` replaces `make start`; polls postgres with nc (up to 10s)
  instead of fixed sleep, kills any running uvicorn before starting fresh
- `make dashboard` kills any running observable preview before restarting
- Update all references in CLAUDE.md, README.md, SCOPE.md, state-hub/README.md,
  and dashboard/src/docs/live-data.md

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

SCOPE.md

@@ -93,7 +93,7 @@ The Custodian is both an **operational system** (State Hub: PostgreSQL + FastAPI
 
 - Start with: `CLAUDE.md` (session protocol) + `README.md` (architecture overview)
 - Key files / directories: `state-hub/` (live API + MCP), `canon/` (governance), `workplans/` (active work), `state-hub/mcp_server/TOOLS.md` (tool reference)
-- Entry points: `cd state-hub && make start` (API); Claude Code with state-hub MCP registered
+- Entry points: `cd state-hub && make backend` (API); Claude Code with state-hub MCP registered
 
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