fix(config_flow): F-B — neither pairing step is a dead end (t33)

protocol_pair and adb_pair now each offer "continue without pairing" (the new
CONF_SKIP_PAIRING form key), so the entry still finishes — in passive mode —
instead of stranding the user on a form with no way forward.

adb_pair: the ADB host/port live ON this form (the user step is gone), a host
typed here is authoritative, the addr the error names is therefore fixable
where the error appears, and skip routes through _async_after_pairing. ADB
stays enabled on purpose: the manager already degrades to its passive,
background-retrying state without a key, and the Pair ADB button (registered
for adb-enabled entries) then pairs later without re-adding the integration.

protocol_pair: the protocol host lives on this form too and a corrected
address restarts the pairing session against it; submitting without a code asks
the Shield for a fresh code (_async_restart_protocol_pairing) instead of
erroring; skip switches the transport off, because an unpaired protocol client
fails auth on its first connect and would only bounce the user into the reauth
flow — a fresh dead end. On reauth the skip aborts with reauth_skipped instead
of faking a repair.

_start_protocol_pairing also returns None now when build_protocol_client does
(androidtvremote2 missing) so the step reports protocol_unavailable instead of
crashing on a None client in the default CI variant.

Verified: uvx --with pytest-asyncio pytest tests -q → 242 passed, 1 skipped;
uvx ruff check custom_components tests → clean. The end-to-end skip-path and
copy tests land with the t33 UX suite commit.

custom_components/nvidia_shield/const.py

@@ -26,6 +26,10 @@ CONF_ADB_PORT = "adb_port"
 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
+# user on a form with no way forward.
+CONF_SKIP_PAIRING = "skip_pairing"
 DEFAULT_PROTOCOL_API_PORT = 6466
 DEFAULT_PROTOCOL_PAIR_PORT = 6467