feat(image): opt-in screen capture as an image entity, binary-safe over ADB

The user asked for "an image entity of the device screen capture? Can that be
added". It is added as `image.<entry>_screen_capture`, and the three boundaries
are the feature:

- it NEVER drives state — the state is the capture timestamp, and the capture
  path reads the ADB poller and nothing else (pinned by a manager that raises on
  any other attribute, and by a real-HA run whose recorded state is the
  timestamp with no bytes anywhere in the attributes);
- it is OPT-IN and OFF by default (`screen_capture_enabled`, Main setup row) —
  with the option absent `async_setup_entry` adds no entity at all;
- it NEVER polls — HA's own `should_poll = False` for image entities is kept, so
  only an image fetch or `homeassistant.update_entity` captures; concurrent
  fetches share one shell and a capture is reused for 5 s.

BINARY-SAFE CAPTURE: `screencap -p | base64` over the existing shell, decoded
locally with `base64.b64decode` and gated on the PNG signature AND the IHDR
chunk. `AdbDevice.shell()` returns `str`, so raw PNG bytes cannot travel through
it; the alternative (a device temp file + the library's file-read path) needs the
raw AdbDevice and writes to the Shield's shared storage, where a crash between
write and delete leaves a screenshot behind. The base64 route leaves no
device-side artifact — nothing to clean up — at the cost of ~33% more bytes on
the wire.

HONEST FAILURES: ADB off / ADB down / a capture that returned no PNG / a
transport that raised all make the entity UNAVAILABLE with `capture_status`
(`adb_disabled` / `adb_disconnected` / `capture_failed`) — never a blank or
zero-byte image. `image_last_updated` moves only on success.

Tests: 25 new cases (a real 2x1 PNG fixture on the wire — bytes, never a str;
every non-PNG answer rejected; disconnected/failed/recovery paths; capture reuse,
coalescing and the expiry window; opt-in default OFF and on) plus 4 config-flow
cases (schema default False, off stays off, on is stored, and it can be turned
back off). The stub harness gains the image platform and `util.dt` faces, the
real-HA entity matrix gains this class, and the drift sweep's coverage test
demanded exactly that. README documents the cost, the opt-in and the boundary.

tests/entity_stublib.py

@@ -7,6 +7,7 @@ their entity module through the synthetic ``nsh`` package AFTER calling
 """
 
 import asyncio
+import datetime
 import enum
 import sys
 import types
@@ -25,6 +26,7 @@ ENTITIES_STUB_NAMES = (
     "homeassistant.components.media_player",
     "homeassistant.components.remote",
     "homeassistant.components.button",
+    "homeassistant.components.image",
     "homeassistant.helpers",
     "homeassistant.helpers.entity_registry",
     "homeassistant.helpers.device_registry",
@@ -33,12 +35,15 @@ ENTITIES_STUB_NAMES = (
     "homeassistant.helpers.redact",
     "homeassistant.helpers.entity",
     "homeassistant.helpers.entity_platform",
+    "homeassistant.util",
+    "homeassistant.util.dt",
     "nsh.helpers",
     "nsh.power",
     "nsh.jellyfin",
     "nsh.media_player",
     "nsh.diagnostics",
     "nsh.remote",
+    "nsh.image",
 )
 
 
@@ -431,6 +436,7 @@ def install() -> None:
         SENSOR="sensor",
         REMOTE="remote",
         BUTTON="button",
+        IMAGE="image",
     )
     sys.modules["homeassistant.const"] = ha_const
 
@@ -463,6 +469,93 @@ def install() -> None:
     sensor_platform.SensorDeviceClass = types.SimpleNamespace(APP="app")
     sys.modules["homeassistant.components.sensor"] = sensor_platform
 
+    # t66: homeassistant.components.image.ImageEntity — the slice the screen
+    # capture entity uses, carrying the REAL contract that matters here: the
+    # attributes HA reads (``content_type``, ``image_last_updated``), the real
+    # ``__init__(hass, verify_ssl=False)`` signature, ``async_image`` as the
+    # bytes seam, state writing as a no-op (the harness writes no states), and
+    # HA 2026.10's own ``_attr_should_poll = False`` ("No need to poll image
+    # entities"). A subclass that forgets its base ``__init__`` fails here too.
+    image_platform = types.ModuleType("homeassistant.components.image")
+
+    class _EntityFace:
+        """The Entity surface HA reads, backed by the ``_attr_*`` convention.
+
+        The real ImageEntity inherits all of this from Entity; the stub carries
+        the properties so a test can READ what the entity publishes (naming,
+        device, polling, availability) without a state machine.
+        """
+
+        _attr_available = True
+        _attr_should_poll = True
+        _attr_translation_key = None
+        _attr_unique_id = None
+        _attr_device_info = None
+        _attr_extra_state_attributes = None
+
+        def async_write_ha_state(self) -> None:
+            return None
+
+        @property
+        def available(self) -> bool:
+            return self._attr_available
+
+        @property
+        def should_poll(self) -> bool:
+            return self._attr_should_poll
+
+        @property
+        def translation_key(self):
+            return self._attr_translation_key
+
+        @property
+        def unique_id(self):
+            return self._attr_unique_id
+
+        @property
+        def device_info(self):
+            return self._attr_device_info
+
+        @property
+        def extra_state_attributes(self):
+            return self._attr_extra_state_attributes
+
+    class ImageEntity(_EntityFace):
+        _attr_content_type = "image/jpeg"
+        _attr_image_last_updated = None
+        _attr_should_poll = False
+
+        def __init__(self, hass, verify_ssl: bool = False) -> None:
+            self.hass = hass
+
+        @property
+        def content_type(self) -> str:
+            return self._attr_content_type
+
+        @property
+        def image_last_updated(self):
+            return self._attr_image_last_updated
+
+        async def async_image(self) -> bytes | None:
+            raise NotImplementedError
+
+    image_platform.ImageEntity = ImageEntity
+    sys.modules["homeassistant.components.image"] = image_platform
+
+    # t66: homeassistant.util.dt — the timestamp helper the image entity stamps
+    # ``image_last_updated`` with. ``utcnow()`` really is UTC-aware, as in HA.
+    ha_util = types.ModuleType("homeassistant.util")
+    ha_util.__path__ = []
+    dt_util = types.ModuleType("homeassistant.util.dt")
+
+    def _utcnow():
+        return datetime.datetime.now(datetime.UTC)
+
+    dt_util.utcnow = _utcnow
+    ha_util.dt = dt_util
+    sys.modules["homeassistant.util"] = ha_util
+    sys.modules["homeassistant.util.dt"] = dt_util
+
 
     helpers = types.ModuleType("homeassistant.helpers")
     entity_registry = types.ModuleType("homeassistant.helpers.entity_registry")
@@ -617,6 +710,9 @@ def load_entity_modules() -> dict:
         # belongs here; tests/test_module_coverage.py sweeps EVERY module, which
         # is what keeps this list from having to be complete.
         "button",
+        # t66: the screen-capture platform is a platform like the others, so it
+        # loads here too (and the module-coverage sweep already walks every file)
+        "image",
         "init",
     ):  # "init" maps the integration __init__.py (t29 G8 async_setup)
         if name == "init" and "nsh.init" in sys.modules:
@@ -633,6 +729,7 @@ def load_entity_modules() -> dict:
             "media_player",
             "remote",
             "diagnostics",
+            "image",
         )
     }