docs: add v0.3.0 changelog entry and network bindings reference (#29)

CHANGELOG.md:
- v0.3.0 Phase 1b entry covering operator console, events feed,
  wizard, session auth, and infrastructure changes

docs/environment.md:
- New "Network and Service Bindings" section documenting:
  - central-gui binds 0.0.0.0 by design (network gating is ops)
  - NATS listener ports table (4222/8080/8222/1883)

Co-authored-by: Matt Johnson <mj@k7zvx.com>

docs/environment.md

@@ -28,6 +28,32 @@ The Windows workstation (matt-desktop) has no Central repository clones.
 The directory `C:\Users\mtthw\central_work\` is scratch space only and
 should not be used for commits.
 
+
+## Network and Service Bindings
+
+### Bind Address
+
+`central-gui` binds to `0.0.0.0` by design. Network gating is the
+operator's responsibility (firewall, Tailscale, etc.), not the app's.
+Do not switch to `127.0.0.1` or to a specific interface — operators
+choose their bind via whatever network they want to expose the service on.
+
+### NATS Listener Ports
+
+The default `nats-server.conf` listens on more than just :4222:
+
+| Port | Protocol | Used by Central? |
+|------|----------|------------------|
+| 4222 | NATS client | Yes (all) |
+| 8080 | WebSocket | No (Phase 0 leftover) |
+| 8222 | HTTP monitoring | No (manual ops only) |
+| 1883 | MQTT | No (Phase 0 leftover) |
+
+None of the unused ports cause active harm — they listen but no consumer
+connects. Operators can remove them from `nats-server.conf` if they want
+a tighter footprint. Documenting so future contributors don't grep for
+"MQTT integration" and come up confused.
+
 ## Repository
 
 | Property | Value |