v1.44.7: plan backgrounds never displayed (regression from v1.44.5)

The card signs content urls because a browser cannot authenticate an <image
href>. But _display() was called inside _buildModel(), and the space model is
memoized on the config fingerprint — so the UNSIGNED url froze in the cache and
the signature, which did arrive, never reached the element. The plan never
loaded, and the browser kept hitting the unsigned path: 401, which Home
Assistant reports as a failed login attempt from the viewer's own IP (that is
how the owner spotted it). PDF links were unaffected: they already resolved at
render time.

- _buildModel() keeps the raw plan_url; the render pass calls _display().
- _display() returns '' for an unsigned content url instead of the plain path,
  and the <image> is not emitted at all until the signature lands — no 401, no
  spurious login-attempt warning.
- _resign() replaces 'drop everything and re-request': the previous urls are
  kept until the new ones arrive, so a wall tablet never blanks.
- demo/smoke_plan_signed.mjs: reproduces on v1.44.6 (href stays ?v=..., never
  ?authSig=), passes here. TESTING.md row added.
- docs: CHANGELOG.md + CHANGELOG.ru.md + STATUS.md.

docs/TESTING.md

@@ -234,6 +234,12 @@ Run the *core flows* (marked ★ below) in each environment at least once per mi
       are only reachable through /api/houseplan/content/… with a session; the
       old /houseplan_files/plans|files paths return 404 after a restart; old
       stored URLs keep working (rewritten on read) [auto+manual]
+- [ ] Signed plan background (v1.44.7): a space whose plan lives on the content
+      endpoint renders its background image with an `authSig` query — the plan is
+      visible after a plain page load, and Home Assistant logs NO failed-login
+      attempt from the viewer's own IP. Nothing is requested before the signature
+      arrives; a 12 h re-sign keeps the previous url until the new one lands
+      [auto: smoke_plan_signed]
 - [ ] Dialog zombies (v1.43.0, audit L3): close a dialog (Esc) while its save is
       in flight and let the save fail — the dialog stays closed, the card keeps
       rendering, the error toast still fires [auto: unit: logic.test + manual]