feat: phase 2 relay implementation

Implement the Axon relay as relay/ (module axon/relay). Includes:
- WebSocket framing (RFC 6455, no external deps) in relay/websocket/
- Per-connection auth: challenge/response with ed25519 + allowlist check
- Ingest pipeline: sig verify, dedup, ephemeral fanout, SQLite persistence
- Subscription manager with prefix-matching filter fanout in relay/subscription/
- SQLite storage with WAL/cache config and UNION query builder in relay/storage/
- Graceful shutdown on SIGINT/SIGTERM
- Filter/TagFilter types added to axon core package (required by relay)

1 files changed, 22 insertions, 0 deletions

diff --git a/axon.go b/axon.go
index 51ec22d..ebe18a2 100644
--- a/axon.go
+++ b/axon.go
@@ -29,6 +29,28 @@ type Tag struct {
         Values []string `msgpack:"values" json:"values"`
 }
 
+// TagFilter selects events that have a tag with the given name and any of the
+// given values. An empty Values slice matches any value.
+type TagFilter struct {
+        Name   string   `msgpack:"name"`
+        Values []string `msgpack:"values"`
+}
+
+// Filter selects a subset of events. All non-empty fields are ANDed together;
+// multiple entries within a slice field are ORed.
+//
+// IDs and Authors support prefix matching: a []byte shorter than 32 bytes
+// matches any event whose ID (or pubkey) starts with those bytes.
+type Filter struct {
+        IDs     [][]byte    `msgpack:"ids"`
+        Authors [][]byte    `msgpack:"authors"`
+        Kinds   []uint16    `msgpack:"kinds"`
+        Since   int64       `msgpack:"since"` // inclusive lower bound on created_at
+        Until   int64       `msgpack:"until"` // inclusive upper bound on created_at
+        Limit   int32       `msgpack:"limit"` // max events to return (0 = no limit)
+        Tags    []TagFilter `msgpack:"tags"`
+}
+
 // Event is the core Axon data structure. All fields use their wire types.
 // id, pubkey and sig are raw 32/64-byte slices, not hex.
 // content is opaque bytes (msgpack bin type).