feat: multi-clinic Temetro Network with per-clinic identity (v0.8.0)

The relay is now multi-clinic. Each clinic authenticates to the /hub
namespace by signing a challenge with its own Ed25519 clinic signing key
(a per-clinic identity, not a shared RELAY_TOKEN), and the relay routes
every device response back to only the clinic that originated the request
(keyed by requestId) — so clinics never see each other's traffic.

Backend:
- clinic_signing_keys.network_enabled + GET/PUT /api/signing/network
  (owner/admin) to join/leave the network.
- relay-client keeps one authenticated hub connection per network-enabled
  org (connectOrg/disconnectOrg, hubs map keyed by orgId); emitToWallet/
  sendToWallet take orgId; offline flush is org-scoped.
- Wallet import/push return 409 until a clinic joins.
- RELAY_TOKEN is now optional/legacy (open relay needs no shared secret).

Frontend:
- "Join Temetro Network" toggle in Settings → Signing, localized in all
  five languages (en, fr, de, so, ar).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/drizzle/0032_closed_dakota_north.sql

@@ -0,0 +1 @@
+ALTER TABLE "clinic_signing_keys" ADD COLUMN "network_enabled" boolean DEFAULT false NOT NULL;

backend/drizzle/meta/_journal.json

@@ -225,6 +225,13 @@
       "when": 1783117115021,
       "tag": "0031_stiff_gateway",
       "breakpoints": true
+    },
+    {
+      "idx": 32,
+      "version": "7",
+      "when": 1783263738631,
+      "tag": "0032_closed_dakota_north",
+      "breakpoints": true
     }
   ]
 }