chore: bump jsdom to 29.1.1, drop border-radius shorthand workaround (#154)

jsdom 29.1.1 ships two fixes that unblock this:
- 5f66329: Fix background-origin/background-clip in background shorthand
- ad8af77: Fix border shorthand handling

The `resolveBorderRadiusPx` fallback chain (inline-style scan, stylesheet
walk) was only needed because jsdom 29.0.x returned "" for
`style.borderRadius` when the value came from a CSS shorthand rule. With
29.1.1 the computed shorthand value resolves correctly, so the plain
`parseRadiusToPx(style.borderRadius)` path succeeds and the fallbacks
are dead code. Test suite confirms 173/173 unit tests and 23/23 jsdom
fixture tests pass with the simplified function.

Closes jsdom/jsdom#4153 (from our side).

Co-authored-by: Claude <noreply@anthropic.com>

package.json

@@ -62,7 +62,7 @@
     "og-image": "bun run scripts/generate-og-image.js"
   },
   "dependencies": {
-    "jsdom": "29.0.0",
+    "jsdom": "29.1.1",
     "marked": "^16.4.2"
   },
   "optionalDependencies": {