v1.46.6: the detach promise, actually kept this time

v1.46.4 and v1.46.5 documented that detaching a plan leaves the image on disk,
added guards for it, and shipped tests. The guards were never reached: they sit
behind 'not superseded', and a file that left the configuration was called
superseded. From old_refs - new_refs alone, replacing a plan, detaching one and
deleting its space are indistinguishable — so all three deleted the file, at the
moment of the save, before any scheduled pass ever ran.

Every test I wrote for this called collect_plans(d, cfg, cfg): old config equal
to new, i.e. only the scheduled pass. The transition that mattered was never
exercised. Codex reproduced it in four lines.

Classification is by owner now:
  space in both, plan A -> plan B  : the user picked another image -> removed
  space in both, plan -> none      : detached -> kept
  space gone                       : kept (the image was imported; a thirty-day
                                     grace measured from file age is meaningless
                                     anyway, it was uploaded months ago)
  space has a plan, other file     : rejected upload -> 1 h
Attachments follow the same shape: dropped from a device that still exists ->
removed (a trash button promises nothing); device gone -> kept; staging folder
-> 1 h.

Tests: a matrix per rule in the pure module, and — the part that was missing —
test_detaching_a_plan_keeps_the_file, which goes through real config/set calls:
attach, detach, assert the file is there, restart, assert again, re-attach,
replace, assert the replaced one is gone, delete the space, assert the plan
survives. Also strengthened the sweep/save race test to assert the save actually
succeeded and the config points at the specific expected file, per the report.

custom_components/houseplan/const.py

@@ -34,7 +34,7 @@ PLAN_ORPHAN_TTL_S = 3600
 SCHEDULED_GRACE_S = 30 * 24 * 3600
 FILES_DIR = "houseplan/files"
 CONF_ADMIN_ONLY = "admin_only"
-VERSION = "1.46.5"
+VERSION = "1.46.6"
 
 DEFAULT_CONFIG: dict = {
     "spaces": [],