feat(mqtt): publish each zone as its own HA device under the panel

[brettmeyerowitz]

Problem

Every entity PAI publishes lands on a single Home Assistant device — the panel. On a system with a few dozen zones that is one device holding several hundred entities in a flat, ungrouped list, and there is no way to see "everything about the front door" in one place.

Change

Zones get their own device block, linked back to the panel with via_device so Home Assistant nests them underneath it. Partitions, PGMs and system entities are untouched.

Before — every zone entity:

"device": {
  "manufacturer": "Paradox", "model": "EVO192",
  "identifiers": ["Paradox_aabbccdd"],
  "name": "EVO192", "sw_version": "6.80 build 5"
}

After — a zone entity:

"device": {
  "manufacturer": "Paradox", "model": "Zone",
  "identifiers": ["Paradox_aabbccdd_zone_Front_Door"],
  "name": "Front Door",
  "via_device": "Paradox_aabbccdd"
}

The zone's binary sensor, numeric sensors and bypass switch all resolve to the same device, so they group together.

Migration safety

unique_id is deliberately not touched. On an existing install Home Assistant re-parents the entities in place rather than re-creating them — entity ids, customisations and recorder history are all preserved. The only visible change is where they sit in the device tree.

The zone identifier is scoped by panel serial (Paradox_<serial>_zone_<key>) to match the convention the panel device adopted in #592, so two panels on one broker cannot collide. Zone key is label-derived, so renaming a zone on the panel changes its identifier — that is the same pre-existing caveat that already applies to unique_id, not something this change introduces.

Testing

• tests/interfaces/mqtt/test_entities.py — the two zone serialization tests now assert the nested device block; verified they fail without the source change.
• tests/interfaces/mqtt/test_homeassistant.py — extended the end-to-end discovery test with a zone, asserting the published payload including via_device.
• Full suite: 1700 passed. flake8 --select=E9,F63,F7,F82 clean, black/isort clean.

Functionally this has been running against an MG5050 since July. The deployed build used an unscoped Paradox_zone_<key> identifier; this PR scopes it by serial per the note above, which is the only difference from what has been exercised in production.

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

🟢 Approval recommended

No unresolved issues were identified, and the changes are covered by tests.

Pull request overview

Adds Home Assistant device nesting so each zone appears as its own device beneath the panel while preserving entity identities.

Changes:

• Adds serial-scoped zone devices linked with via_device.
• Preserves existing panel and entity identifiers.
• Updates unit and integration tests.

File summaries

File	Description
tests/interfaces/mqtt/test_homeassistant.py	Verifies the published zone discovery payload.
tests/interfaces/mqtt/test_entities.py	Verifies zone device serialization.
paradox/interfaces/mqtt/entities/abstract_entity.py	Generates zone-specific device metadata.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 0
• Review effort level: Lite

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