Prepare v1.74.0

Seven version sources move together to 1.74.0; both changelogs gain the
stable section aggregated from the previous stable v1.73.0, the release
notes carry three itemised bullets on each side plus the grouped
small-fixes bullet, and STATUS says what this release is.

What the user gets since v1.73.0: the plan is noticeably smoother and in
Firefox dramatically so — a pan frame now moves what is already drawn by
a composited transform with the scene re-rasterizing on a budget (#531),
and a marker shadow sized in container units no longer restarts a
non-composited animation on every marker at once (#524); the printed plan
is about a third larger, because the in-plan dimension labels shrank and
the separate column of external dimensions is gone (#530); a plan left
over from the era of rooms without walls can be edited again, the
leftover cleaned up on the first save instead of refusing every change
(#529, reported in #527). Grouped under small fixes: alignment guides
follow the gesture again (#521), the summary panel neither freezes the
first frame nor claims an unavailable source (#509) and its settings
dialog scrolls again (#508), a space switch no longer replays a
neighbouring door's leaf (#525), and the card downloads 12.8 KB less on a
cold start (#526).

The speed verdict for #531 is deliberately not claimed here: headless
Firefox and Chromium hold 60 fps on both the old and the new path, so it
is owed by a profile from the owner's machine on the same pan.

`npm test` 2528/0/1 skip, `pytest tests_backend` 467 passed, release
notes pass the #328 verifier against v1.73.0..HEAD, bundle 287 242 B gzip
inside the ceiling, docs strict green.

Issue: #531
User-Visible: yes
Release: v1.74.0

package.json

@@ -1,6 +1,6 @@
 {
   "name": "houseplan-card",
-  "version": "1.74.0-beta.3",
+  "version": "1.74.0",
   "description": "Interactive house plan Lovelace card for Home Assistant",
   "license": "MIT",
   "type": "module",