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

third_party/certspotter/CTCLOUD_PATCH.md

@@ -0,0 +1,53 @@
+# ctcloud patch to upstream CertSpotter
+
+This directory is a copy of upstream CertSpotter
+(https://github.com/SSLMate/certspotter), pulled in as a local module and
+wired up with a `replace` directive in the root `go.mod`.
+
+It is intentionally a copy (not a git submodule) so the patched tree lives in
+this repository and is compiled by the Docker build with no network access to a
+separate fork. To rebase on a newer upstream release:
+
+1. Replace this directory with the new upstream tree.
+2. Re-apply the two hunks below.
+
+## Changes (only two hunks)
+
+### `monitor/config.go`
+
+Adds an exported `IdentifierSink` interface and a `Config.IdentifierSink`
+field:
+
+```go
+type IdentifierSink interface {
+	HandleIdentifiers(ctx context.Context, identifiers *certspotter.Identifiers)
+}
+```
+
+### `monitor/process.go`
+
+In `processCertificate`, immediately after `certInfo.ParseIdentifiers()`, hand
+the parsed identifiers to the sink and return, bypassing the watchlist,
+certificate-chain retrieval and notification paths:
+
+```go
+if config.IdentifierSink != nil {
+	config.IdentifierSink.HandleIdentifiers(ctx, identifiers)
+	return nil
+}
+```
+
+## Why
+
+The sink gives ctcloud parsed DNS identifiers via a direct in-process Go call:
+
+```text
+CT log entry -> CertSpotter parse -> IdentifierSink.HandleIdentifiers -> classifier
+```
+
+No stdout, no JSON, no files, no hooks, no subprocess. Setting the sink also
+skips issuer-chain fetching and the watchlist machinery, which is exactly the
+I/O and serialization overhead the design forbids.
+
+Upstream is otherwise unmodified. License and notices are preserved in
+`LICENSE`.