ctcloud: CertSpotter-backed CT cloud-resource monitor

Single stateless Go process that consumes CT logs via embedded (patched)
CertSpotter internals, classifies cloud/database/storage DNS identifiers
in-process with a zero-allocation classifier, enriches via round-robin DNS
resolvers with CNAME following, and batch-writes useful findings to PostgreSQL.

- third_party/certspotter: 2-hunk IdentifierSink patch, no stdout/JSON/files
- internal/classify: AWS/Azure/GCP/Firebase/Cloudflare R2/DigitalOcean/Supabase/OCI
- internal/dns: sharded bounded TTL cache, multi-resolver load balancing + failover
- internal/pipeline: bounded queues, dedup, direct-priority load shedding
- internal/store: pgx batch writer, Postgres CT checkpoints (no cert contents)
- internal/probe: optional non-destructive reachability checks (off by default)
- Docker: distroless non-root, read-only rootfs, no app volume, resource limits
- tests enforce 0 allocs/op on the classifier and sink hot path

Dockerfile

@@ -0,0 +1,22 @@
+# syntax=docker/dockerfile:1
+
+FROM golang:1.25-alpine AS build
+WORKDIR /src
+
+# Cache module downloads (including the local certspotter fork's deps).
+COPY go.mod go.sum ./
+COPY third_party/certspotter/go.mod third_party/certspotter/go.sum ./third_party/certspotter/
+RUN go mod download
+
+COPY . .
+
+# Static binary: no cgo, no shell, no writable filesystem required.
+RUN CGO_ENABLED=0 GOOS=linux go build \
+        -trimpath -ldflags="-s -w" \
+        -o /out/ctcloud ./cmd/ctcloud
+
+FROM gcr.io/distroless/static-debian12:nonroot
+COPY --from=build /out/ctcloud /ctcloud
+USER nonroot:nonroot
+EXPOSE 9090
+ENTRYPOINT ["/ctcloud"]