feat(packaging): ship a node firewall profile for inbound WebRTC

The packages carried a profile for LAN casting and none for the node's own
peer traffic, on the reasoning that the node exposes only a loopback admin
API. That is true of its administration surface and false of its transport.

WebRTC binds an ephemeral UDP port per connection, so there is no fixed port
to open, and a connection succeeds only if one side can initiate. Browsers
publish their host candidate as an mDNS `<uuid>.local` name, which aioice
cannot resolve on any platform and discards — so the node can never call a
browser back, and the browser must call the node. A node that refuses
unsolicited inbound UDP is unreachable from every browser on its own LAN,
leaving reflexive candidates, which fail whenever both peers share one public
IP and the router will not hairpin.

Hit twice in one session on two different hosts: a firewalld zone narrowed to
mdns + 19550-19553/tcp, and a ufw host with default deny-incoming. Both
presented as "the app cannot connect", neither as a firewall message.

Passive like the cast profile: packaged, not activated. The guide says to
scope it to a LAN zone or source, including the libvirt case, where traffic
from a guest to its own hypervisor is not masqueraded and so must be scoped
to the guest subnet rather than the LAN.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DtfG7z6wHWj8RKHCvxQtY1

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