fix(ingestion): authenticate the REST API as a whole, not route by route

Only /mcp was wrapped in BearerMiddleware; /query, /write, /ingest*,
/promote, /pending and the rest on the same mux had no auth, and
infra#517 found them on the internet (mitigated there by narrowing the
ingress). They are still open on the tailnet and LAN NodePort 30330.

mountREST puts the REST routes on their own mux, mounted at "/" behind
the same bearer middleware and credential as /mcp. Routes registered on
the outer mux stay explicitly public (/mcp has its own auth, /capture,
the HMAC webhook, OAuth metadata, /metrics); anything else, including a
route added later, is authenticated by default.

The hyperguild CLI (cmd/hyperguild and internal/brain) now sends
BRAIN_MCP_TOKEN, which it never did. brain-ui and brain-ingest-ntfy
already send theirs.

Refs #149

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ingestion/cmd/server/routes.go

@@ -0,0 +1,30 @@
+package main
+
+import (
+	"net/http"
+
+	"github.com/mathiasbq/hyperguild/ingestion/internal/api"
+)
+
+// mountREST registers the REST API on its own mux and mounts it at "/" behind
+// auth (hyperguild#149). Authentication is a property of the mux, not of each
+// route: anything not registered on the outer mux as explicitly public (/mcp,
+// /capture, the HMAC webhook, OAuth metadata, /metrics) lands here and is
+// authenticated, including routes added later. Before this, only /mcp was
+// wrapped, and the REST routes beside it were open; infra#517 found them on
+// the internet.
+func mountREST(mux *http.ServeMux, h *api.Handler, auth func(http.Handler) http.Handler) {
+	rest := http.NewServeMux()
+	rest.HandleFunc("POST /query", h.Query)
+	rest.HandleFunc("POST /write", h.Write)
+	rest.HandleFunc("POST /index", h.Index)
+	rest.HandleFunc("POST /ingest", h.Ingest)
+	rest.HandleFunc("POST /ingest-path", h.IngestPath)
+	rest.HandleFunc("POST /ingest-raw", h.IngestRaw)
+	rest.HandleFunc("POST /backfill-refs", h.BackfillRefs)
+	rest.HandleFunc("GET /pending", h.Pending)
+	rest.HandleFunc("POST /promote", h.Promote)
+	rest.HandleFunc("POST /backfill-embeddings", h.BackfillEmbeddings)
+	rest.HandleFunc("GET /pass-rate", h.PassRate)
+	mux.Handle("/", auth(rest))
+}