Stage 7: Dockerfile, integration tests, updated README

Dockerfile:
- Multi-stage build (golang:1.25-alpine → scratch)
- CGO_ENABLED=0, static binary, stripped with -ldflags="-w -s" (~11 MB)

Tests (13 cases, internal/api/api_test.go):
- Auth middleware: missing token, invalid token, valid token
- Bootstrap idempotency (second call → 403)
- Alert upsert: same fingerprint updates row; different fingerprints add rows
- Acknowledge: set and clear, verified via GET
- Comment ownership: only author can delete own comment (404 for others)
- Schedule conflict: duplicate date → 409; multi-date rollback on partial conflict
- Stats: totals, by-hour returns 24 slots, by-day returns 7 slots

README: quick start, Docker, env vars, Alertmanager config, full API reference

Dockerfile

@@ -0,0 +1,11 @@
+FROM golang:1.25-alpine AS builder
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 GOOS=linux go build -ldflags="-w -s" -o /terdut ./cmd/terdut
+
+FROM scratch
+COPY --from=builder /terdut /terdut
+EXPOSE 8080
+ENTRYPOINT ["/terdut"]