HS: resize observer mock + on resize (+3 tests)

Cluster 26. Three parts:
(a) `tests/hs-run-filtered.js`: mock style is now a Proxy that dispatches
    a synthetic `resize` DOM event on the owning element whenever
    `width` / `height` changes (via `setProperty` or direct assignment).
    Detail carries numeric `width` / `height` parsed from the current
    inline style. Strengthens the old no-op ResizeObserver stub into an
    `HsResizeObserver` class with a per-element callback registry
    (collision-proof name vs. cluster 27's IntersectionObserver); HS's
    `on resize` uses the plain DOM event path, not the observer API.
    Adds `ResizeObserverEntry` for code that references it.
(b) `tests/playwright/generate-sx-tests.py`: new pattern for
    `(page.)?evaluate(() => [{] document.{getElementById|querySelector}(…).style.PROP = 'VAL'; [}])`
    emitting `(host-set! (host-get target "style") "PROP" "VAL")`.
(c) `spec/tests/test-hyperscript-behavioral.sx`: regenerated — the three
    resize fixtures now carry the style mutation step between activate
    and assert.

No parser/compiler/runtime changes: `on resize` already parses via
`parse-compound-event-name`, and `hs-on` binds via `dom-listen` which is
plain `addEventListener("resize", …)`.

Suite hs-upstream-resize: 0/3 → 3/3. Smoke 0-195: 164/195 → 165/195
(the +1 smoke bump is logAll-generator work uncommitted in the main tree
at verification time, unrelated to this cluster).

spec/tests/test-hyperscript-behavioral.sx

@@ -10440,6 +10440,7 @@
       (dom-append (dom-body) _el-box)
       (dom-append (dom-body) _el-out)
       (hs-activate! _el-box)
+      (host-set! (host-get (dom-query-by-id "box") "style") "width" "200px")
       (assert= (dom-text-content (dom-query-by-id "out")) "200")
     ))
   (deftest "provides height in detail"
@@ -10452,6 +10453,7 @@
       (dom-append (dom-body) _el-box)
       (dom-append (dom-body) _el-out)
       (hs-activate! _el-box)
+      (host-set! (host-get (dom-query-by-id "box") "style") "height" "300px")
       (assert= (dom-text-content (dom-query-by-id "out")) "300")
     ))
   (deftest "works with from clause"
@@ -10464,6 +10466,7 @@
       (dom-append (dom-body) _el-box)
       (dom-append (dom-body) _el-out)
       (hs-activate! _el-out)
+      (host-set! (host-get (dom-query-by-id "box") "style") "width" "150px")
       (assert= (dom-text-content (dom-query-by-id "out")) "150")
     ))
 )