v1.47.0: pick a plan you already uploaded

Closes both findings from the v1.46.6 review with one feature, because they are
the same gap seen from two sides. HP-1466-02: a detached plan stayed on disk and
could not be re-attached from the card — the old url is nowhere in the config,
and the backend test 'proved' reattach by remembering it in a Python variable.
HP-1466-01: files kept forever with no way to see or remove them is not a
policy, it is accumulation.

New: houseplan/plans/list (name, url, size, modified, and which spaces use it)
and houseplan/plans/delete, which refuses while a space still references the
file — the stored configuration answers that, not the client. In the space
dialog, 'Already uploaded' shows the list with thumbnails; one click attaches,
reading the aspect from the image as an upload does; the trash button is the
only way a plan file is ever deleted.

That also bounds the disk without any timer, which is the part every automatic
attempt got wrong: v1.46.4 deleted detached plans, v1.46.5 raced the retry that
was about to reference an upload. The user decides, and can now see what they
are deciding about.

Docs: comments in plans.py and websocket_api.py still described the age-based
collection v1.46.6 removed (report §6); ARCHITECTURE gained the two new routes
and an explanation of why the listing is what makes 'never delete' livable.

custom_components/houseplan/const.py

@@ -31,7 +31,7 @@ PLAN_ORPHAN_TTL_S = 3600
 SCHEDULED_GRACE_S = 30 * 24 * 3600
 FILES_DIR = "houseplan/files"
 CONF_ADMIN_ONLY = "admin_only"
-VERSION = "1.46.6"
+VERSION = "1.47.0"
 
 DEFAULT_CONFIG: dict = {
     "spaces": [],