fix(photon): support E.164 and DM GUID targets for home channel

Allow PHOTON_HOME_CHANNEL to accept a bare E.164 phone number or a
`any;-;+1...` DM chat GUID in addition to a Spectrum space id. Inbound
DM spaces are cached so replies resolve without a second SDK lookup,
and `photon` is added to _PHONE_PLATFORMS so send_message treats E.164
strings as explicit targets rather than falling through to channel-name
resolution.

tests/tools/test_send_message_target_parse.py

@@ -0,0 +1,20 @@
+"""Parser-only tests for send_message targets.
+
+These stay separate from ``test_send_message_tool.py`` because that module
+skips wholesale when optional Telegram dependencies are not installed.
+"""
+
+from tools.send_message_tool import _parse_target_ref
+
+
+def test_photon_e164_target_is_explicit() -> None:
+    chat_id, thread_id, is_explicit = _parse_target_ref("photon", "+15551234567")
+
+    assert chat_id == "+15551234567"
+    assert thread_id is None
+    assert is_explicit is True
+
+
+def test_e164_target_still_requires_phone_platform() -> None:
+    assert _parse_target_ref("matrix", "+15551234567")[2] is False
+