feat(docker-watcher): phase 11 - frontend embed & SSE

Embed SvelteKit static build in Go binary via go:embed. Event bus
for pub/sub with deploy log, instance status, and deploy status events.
SSE endpoints for real-time streaming. Frontend SSE client with
exponential backoff reconnection. Makefile for build pipeline.
Update Phase 12 auth plan with OAuth2/OIDC support.

web.go

@@ -0,0 +1,9 @@
+package dockerwatcher
+
+import "embed"
+
+// WebBuildFS holds the embedded SvelteKit static build output.
+// The build directory is populated by running `npm run build` in the web/ directory.
+//
+//go:embed web/build
+var WebBuildFS embed.FS