refactor(config): one Shield IP field for both transports (t41)

The two address fields were the same Shield spelled twice, and every bug in the
zeroconf/IP-change path came from keeping them in sync. One field now:

* const.CONF_HOST replaces CONF_ADB_HOST / CONF_PROTOCOL_HOST in the setup form,
  the options page, the pairing forms, the reconfigure/reauth seeding and the
  description copy. ADB port 5555 stays the only port field;
* helpers.entry_host(entry) is the single resolver (options first, then data);
  resolve_adb_config and the protocol settings both go through it, so both
  transports read the same value at call time (the t32 F1 factory re-read keeps
  working: the NEXT built poller sees the new address);
* helpers.seed_host / seed_adb_enabled own the YAML seed's shape rule. A block
  may use `host` or the legacy protocol_host/adb_host keys — t41 keeps the old
  spelling working — and t32 F4's outcome is unchanged: a protocol-only block
  leaves ADB off, an address (or an explicit adb_enabled) turns it on;
* the zeroconf IP-change path collapses the t21-F2 per-host dance into one rule:
  the discovery address IS the entry's address, so the entry is updated when it
  differs and left alone when it matches. The blank-self-heal and
  deliberately-different-ADB-host cases are gone with the duplication — a
  second address field cannot express them anymore, and the tests now pin that
  (previously "an explicit override is never clobbered");
* the options page exposes the protocol toggle it never had (the page could turn
  ADB off but not the protocol);
* button.py (granted to this task) reads the entry's own address instead of
  another integration's entity.

The v3 entry migration that maps existing adb_host/protocol_host onto CONF_HOST
and drops the androidtv key lands in the next commit; HA runs migrations before
setup, so an existing entry is never read with the old shape.

Verified: 311 passed / 2 skipped, 312 / 1 with androidtvremote2, ruff clean,
drift engine exit 0 on HEAD. The UI-copy contract tests (every rendered field
has a label in strings.json AND translations/en.json, key trees identical, host
errors name the field) drove the string edits.

custom_components/nvidia_shield/const.py

@@ -12,6 +12,16 @@ from .ha_adb_common.const import (  # noqa: F401
 
 DOMAIN = "nvidia_shield"
 
+# t41: the INTEGRATION's address field — one Shield IP for the whole stack
+# (protocol + ADB). The two keys below it are LEGACY: a YAML seed may still
+# carry them and the v3 entry migration maps them onto CONF_HOST, but no
+# runtime code reads them.
+CONF_HOST = "host"
+CONF_ADB_HOST = "adb_host"
+CONF_PROTOCOL_HOST = "protocol_host"
+
+# t41 legacy: dropped from entries by the v3 migration (the androidtv entity
+# path it configured is gone), never read at runtime.
 CONF_ANDROIDTV_ENTITY = "androidtv_entity"
 CONF_JELLYFIN_ENTITY = "jellyfin_entity"
 CONF_RECEIVER_ENTITY = "receiver_entity"
@@ -19,12 +29,10 @@ CONF_RECEIVER_INPUT = "receiver_input"
 CONF_POWER_ENTITY = "power_entity"
 CONF_ADB_ENABLED = "adb_enabled"
 CONF_ADB_STORE_APP_INFO = "adb_store_app_info"
-CONF_ADB_HOST = "adb_host"
 CONF_ADB_PORT = "adb_port"
 
 # Remote-protocol transport (androidtvremote2) — Phase 2
 CONF_PROTOCOL_ENABLED = "protocol_enabled"
-CONF_PROTOCOL_HOST = "protocol_host"
 CONF_PAIRING_CODE = "pairing_code"
 # t33 F-B: the "continue without pairing" escape offered on BOTH pairing
 # steps — the entry still finishes (passive mode) instead of stranding the