Add package comments for staticcheck's ST1000

The lint job runs with checks:all, which enables ST1000 (each
package needs a doc comment). Give all six packages concise
package comments; validated locally with -checks all.

internal/apex/apex.go

@@ -1,3 +1,6 @@
+// Package apex canonicalizes DNS names (IDNA, wildcards, case) and
+// derives the registrable eTLD+1 they belong to using the embedded
+// Public Suffix List.
 package apex
 
 import (

internal/loglist/loglist.go

@@ -1,3 +1,6 @@
+// Package loglist fetches and merges the public Certificate
+// Transparency log lists (Chrome's v3 lists and Apple's), normalizing
+// per-log state and endpoints for consumers.
 package loglist
 
 import (

internal/rfc6962/client.go

@@ -1,3 +1,6 @@
+// Package rfc6962 implements the RFC 6962 pieces subidx needs: a CT
+// log client with pinned-key signed tree head verification, entry
+// decoding, and Merkle inclusion proof checking.
 package rfc6962
 
 import (

internal/server/server.go

@@ -1,3 +1,6 @@
+// Package server serves the read-only search API in front of the
+// store, with per-IP rate limiting, Host allow-listing, and bounded
+// result sizes.
 package server
 
 import (

internal/store/store.go

@@ -1,3 +1,6 @@
+// Package store implements the on-disk subdomain index on top of
+// Pebble: a single-writer ingest loop, crash-safe watermarks committed
+// atomically with records, and scan/top queries.
 package store
 
 import (

internal/tailer/tailer.go

@@ -1,3 +1,6 @@
+// Package tailer watches Certificate Transparency logs: it verifies
+// signed tree heads, binds fetched entries to them via inclusion
+// proofs, and feeds decoded names into the store.
 package tailer
 
 import (