feat: add SQLite storage layer with binary-first event persistence

Storage implementation:
- Concrete type with constructor (consumer-side interfaces)
- Event storage: protobuf + zstd-compressed canonical JSON
- Schema: events, deletions, replaceable_events, auth_challenges, rate_limits
- WAL mode, STRICT typing, optimized indexes
- Methods: StoreEvent, GetEvent, GetEventWithCanonical, DeleteEvent

Dependencies:
- modernc.org/sqlite v1.45.0 (pure Go SQLite driver)
- github.com/klauspost/compress v1.18.4 (zstd compression)

366 lines, 10 tests passing

1 files changed, 11 insertions, 0 deletions

diff --git a/go.mod b/go.mod
index e3287d7..03667f7 100644
--- a/go.mod
+++ b/go.mod
@@ -4,16 +4,27 @@ go 1.24.0
 
 require (
         github.com/btcsuite/btcd/btcec/v2 v2.3.2
+        github.com/klauspost/compress v1.18.4
         google.golang.org/grpc v1.79.1
         google.golang.org/protobuf v1.36.11
+        modernc.org/sqlite v1.45.0
 )
 
 require (
         github.com/btcsuite/btcd/chaincfg/chainhash v1.0.1 // indirect
         github.com/decred/dcrd/crypto/blake256 v1.0.0 // indirect
         github.com/decred/dcrd/dcrec/secp256k1/v4 v4.0.1 // indirect
+        github.com/dustin/go-humanize v1.0.1 // indirect
+        github.com/google/uuid v1.6.0 // indirect
+        github.com/mattn/go-isatty v0.0.20 // indirect
+        github.com/ncruces/go-strftime v1.0.0 // indirect
+        github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
+        golang.org/x/exp v0.0.0-20251023183803-a4bb9ffd2546 // indirect
         golang.org/x/net v0.48.0 // indirect
         golang.org/x/sys v0.39.0 // indirect
         golang.org/x/text v0.32.0 // indirect
         google.golang.org/genproto/googleapis/rpc v0.0.0-20251202230838-ff82c1b0f217 // indirect
+        modernc.org/libc v1.67.6 // indirect
+        modernc.org/mathutil v1.7.1 // indirect
+        modernc.org/memory v1.11.0 // indirect
 )