feat: initial Beta 1 release

- soju raw connector with event playback and CHATHISTORY fallback
- SQLite store with msgid de-dup and retention job
- Mentions + Pushover + tuning; structured JSON logs
- Summaries: concise, link-following, multi-line grouping
- HTTP: /healthz, /ready, /tail, /trigger, /metrics
- Docker: distroless, healthcheck, version metadata
- Docs: README, CHANGELOG, compose

internal/notifier/notifier.go

@@ -0,0 +1,8 @@
+package notifier
+
+import "context"
+
+type Notifier interface {
+	Notify(ctx context.Context, title, message string) error
+}
+