Preserve machine identity based on hardware

- Add by_tenant_hostname index for hostname-based lookup
- Add third search in register mutation for hardware matching
- Search by hostname + MAC/serial when fingerprint/email differ
- Fallback to MAC/serial match across all tenant machines
- Preserves ticket history when user changes on same physical machine

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

convex/schema.ts

@@ -647,6 +647,7 @@ export default defineSchema({
     .index("by_tenant_company", ["tenantId", "companyId"])
     .index("by_tenant_fingerprint", ["tenantId", "fingerprint"])
     .index("by_tenant_assigned_email", ["tenantId", "assignedUserEmail"])
+    .index("by_tenant_hostname", ["tenantId", "hostname"])
     .index("by_auth_email", ["authEmail"]),
 
   usbPolicyEvents: defineTable({