fix(config_flow): F-A/F-A2/F-D — the discovered host and the 5555 port ride the schema KEY defaults (t33)

F-A (HIGH): _user_schema_dict re-declared vol.Optional(CONF_ADB_HOST) /
CONF_PROTOCOL_HOST inside `if "host" in defaults:` — a no-op, because
voluptuous keys compare by field name and the first (defaultless) key object
survives. The discovered address therefore never reached the form, and the
user submitted a blank host. The host keys are now declared WITH default=host
(_host_field_key), so a discovery-driven user step arrives pre-filled.

F-A2: a discovery-driven user step says the address is known
("{discovery_note}Discovered Shield at <host> — its address is already filled
in below. ") through description_placeholders, and the no_state_source
re-render keeps the prefill instead of rebuilding a blank schema.

F-D: the ADB port is declared with default=DEFAULT_ADB_PORT (5555), and a YAML
seed's port hint is carried into the form instead of being flattened to 5555.
The seed host now feeds _seed_host (same prefill, no discovery claim).

Reproduce-through-test: tests/voluptuous_mirror.py mirrors the real
voluptuous.Marker key contract (hash/eq by field name, default=UNDEFINED when
omitted), because voluptuous is not installed in either CI variant and the old
bare-key stubs could not tell a schema WITH a default from one without. The
pre-t33 discovery assertion only checked the stored attribute and stayed green
while the form rendered blank; it now reads the schema keys and fails on the
pre-fix code (8 tests reproduced red locally).

Verified: uvx --with pytest-asyncio pytest tests -q → 242 passed, 1 skipped;
uvx ruff check custom_components tests → clean.

tests/entity_stublib.py

@@ -11,6 +11,8 @@ import enum
 import sys
 import types
 
+import voluptuous_mirror
+
 ENTITIES_STUB_NAMES = (
     "voluptuous",
     "homeassistant",
@@ -115,9 +117,9 @@ def install() -> None:
         return
 
     vol = types.ModuleType("voluptuous")
-    vol.Required = lambda key, default=None: key
-    vol.Optional = lambda key, default=None: key
-    vol.Schema = lambda schema: schema
+    # t33 F-A: the faithful mirror keeps schema defaults visible — a bare-key
+    # stub cannot tell a schema WITH a default from one without.
+    voluptuous_mirror.install(vol)
     sys.modules["voluptuous"] = vol
 
     ha = types.ModuleType("homeassistant")
@@ -148,12 +150,16 @@ def install() -> None:
             # t32 F2 (audited helper): recording no-op at hub scope
             pass
 
-        def async_show_form(self, *, step_id, data_schema=None, errors=None):
+        def async_show_form(
+            self, *, step_id, data_schema=None, errors=None,
+            description_placeholders=None,
+        ):
             return {
                 "type": "form",
                 "step_id": step_id,
                 "errors": dict(errors or {}),
                 "data_schema": data_schema,
+                "description_placeholders": dict(description_placeholders or {}),
             }
 
         def async_create_entry(self, *, title, data, options=None):