Key devices on the OCF device ID instead of the serial number

Two Samsung air purifiers of the same model report the identical, well
formed serialNum `BS7SP9AW400114A` (issue #381). Since the entry's
unique_id, the device registry identifiers and every entity unique_id
were all minted from that string, the second unit was refused as already
configured, and would have collided entity-for-entity even if it hadn't
been.

This is the third firmware family to ship an unusable serialNum, after
`Nothing(SVC)` (#83) and the flash-unset sentinel (#189), and the first
one no heuristic can catch: the value is well formed, it's just shared.
`is_placeholder_serial` was a dead end.

So identity moves onto /oic/d's `di`, falling back to /oic/p's `pi`, then
the serial, then the host. `di` is what the protocol already uses to
address the endpoint -- if it were wrong or shared, OCF discovery and the
DTLS association wouldn't work at all -- and it's device-scoped, where
`pi` is platform-scoped and would be shared by a board hosting several
logical devices. Both units in #381 report a distinct `di`. A board that
answers neither resource lands exactly where it did before, so no
existing hardware regresses.

The re-key can't happen in async_migrate_entry: the UUID is only readable
from the device, and an entry can load entirely from its snapshot while
the appliance is off (#295). So v3 -> v4 only records the legacy key, and
the coordinator adopts the UUID on the first live poll, rewriting the
entity registry, the device registry (including subdevice identifiers)
and the entry's unique_id together. Rewriting rather than recreating is
what lets a user keep entity_ids, names, areas, statistics and every
automation that references them.

Three rules keep that adoption from misfiring:

- A poll that reads no UUID never demotes a UUID-keyed entry back onto
  its serial, so one failed reconnect doesn't re-key every entity.
- A changed UUID is followed only when the serial still corroborates it
  (a factory reset may regenerate `di`) or when the entry was keyed on
  its IP, which was never an identity to defend.
- When the identity is rejected as a different appliance, the serial
  isn't adopted either -- otherwise the intruder would gain exactly the
  corroboration needed to win the next poll.

Also stop redacting `di`/`pi` from diagnostics. They're randomly assigned
per-unit UUIDs, not account data, and blanking them is what made the
first #381 diagnostics download unable to answer the only question it was
requested to answer. The owner-set device name stays redacted.

Fixes #381

README.md

@@ -85,7 +85,7 @@ This repo doesn't include the needed CA bundle. For an example of how to obtain
 5. The flow sends a DTLS `ClientHello` to every port in the `49152-49160` range at once and keeps the one that answers -- a real DTLS server identifies itself in about one round trip, and the probe stops there, so nothing is left behind on the appliance. Only that port is then given a real certificate handshake: it fetches the current UUID from Samsung's cloud gateway, mints a leaf cert signed by your CA, and reads the device's identity and `/device/0`. On success it creates the config entry, already knowing the appliance's serial, model, and type.
 6. Every subsequent device only asks for the host IP. The stored CA credentials are reused, and so is the leaf cert itself -- every appliance accepts the same one -- so adding a second appliance doesn't depend on Samsung's cloud being reachable at all. If a device rejects the reused cert (the UUID behind it does rotate), the flow mints a fresh one and retries by itself.
 
-Entities appear under one HA device per appliance, named for the appliance's type and model. Rename freely: the device is keyed on its serial, not its name.
+Entities appear under one HA device per appliance, named for the appliance's type and model. Rename freely: the device is keyed on the appliance's own OCF device ID, not its name. (Some Samsung models ship the same serial number on every unit of a model, so the serial can't tell two of them apart -- the OCF device ID can.)
 
 ---
 
@@ -237,7 +237,8 @@ docker-compose.yml / ha_config/   Local HA dev environment
 If your appliance's type isn't recognized, or it exposes resources this integration doesn't model yet, a Repairs
 issue appears under Settings > System > Repairs pointing you at Settings > Devices & Services > this device >
 the menu > Download diagnostics. That download is already redacted of account/network identifiers (Bixby login
-email, access tokens, device IDs, MAC addresses, serial numbers) before it's generated, so it's safe to attach
+email, access tokens, hashed device IDs, MAC addresses, serial numbers, and the owner-set device name) before it's
+generated, so it's safe to attach
 directly to a new issue using the linked device-support template. This is the fastest way to help add or expand
 support for hardware the maintainers don't have.