Phase 0: skeleton, config, chi router, /healthz

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

CLAUDE.md

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+# QBank
+   
+See PLAN.md for the full execution plan. Work through phases in order.
+Don't skip ahead — each phase has an acceptance test that must pass before
+moving on.
+
+## Conventions
+- Go 1.22+, pure-Go deps only (no CGo).
+- All DB access through internal/db/repo.go.
+- Run `go vet ./...` and `go test ./...` before declaring a phase done.
+- Commit at the end of each phase with message "Phase N: <summary>".
+
+## Commands
+- `make run` — start the dev server
+- `make tailwind` — rebuild CSS
+- `make test` — run all tests