fix(cdp): fire onChange for React/Vue controlled inputs (#353)

Typing over CDP into a React controlled input never fired onChange, so
the value never reached component state (issue #324). Two root causes,
both needed:

1. Value tracker. React/Preact/Vue install a value tracker by redefining
   `value` on the element instance to record the last value they wrote.
   obscura's CDP typing assigned `el.value = ...` directly, which runs
   that wrapper and keeps the tracker in sync, so React saw no change on
   the input event. Synthetic value/backspace writes now go through a new
   __obscura_setFieldValue helper that writes via the element's prototype
   setter, bypassing the tracker. The tracker stays stale, so the input
   event reads as a real edit.

2. Event handler feature detection. React decides whether to use the
   modern `input` event via `("oninput" in document)`. obscura exposed the
   GlobalEventHandlers on* attributes only on window, so that check failed
   and React fell back to a legacy change-detection path that ignores
   input events. The on* attributes are now also present on Document and
   Element, matching the HTML spec (GlobalEventHandlers is mixed into
   Window, Document, and HTMLElement).

Verified end to end over CDP against the real React 18 UMD build: typing
into controlled inputs updates state, the component re-renders, and a
submit handler reads the captured values.

Closes #324.

crates/obscura-cdp/src/domains/input.rs

@@ -14,12 +14,12 @@ fn insert_text_js(escaped_text: &str) -> String {
             var v = t.value || '';\
             var s = t.selectionStart, e = t.selectionEnd;\
             if (s == null) {{\
-                t.value = v + '{text}';\
+                globalThis.__obscura_setFieldValue(t, 'value', v + '{text}');\
             }} else {{\
                 s = Math.max(0, Math.min(s, v.length));\
                 e = (e == null) ? s : Math.max(0, Math.min(e, v.length));\
                 var lo = Math.min(s, e), hi = Math.max(s, e);\
-                t.value = v.slice(0, lo) + '{text}' + v.slice(hi);\
+                globalThis.__obscura_setFieldValue(t, 'value', v.slice(0, lo) + '{text}' + v.slice(hi));\
                 var caret = lo + ('{text}').length;\
                 t.setSelectionRange(caret, caret);\
             }}\
@@ -39,16 +39,16 @@ const BACKSPACE_JS: &str = "(function() {\
     var v = t.value || '';\
     var s = t.selectionStart, e = t.selectionEnd;\
     if (s == null) {\
-        t.value = v.slice(0, -1);\
+        globalThis.__obscura_setFieldValue(t, 'value', v.slice(0, -1));\
     } else {\
         s = Math.max(0, Math.min(s, v.length));\
         e = (e == null) ? s : Math.max(0, Math.min(e, v.length));\
         if (s !== e) {\
             var lo = Math.min(s, e), hi = Math.max(s, e);\
-            t.value = v.slice(0, lo) + v.slice(hi);\
+            globalThis.__obscura_setFieldValue(t, 'value', v.slice(0, lo) + v.slice(hi));\
             t.setSelectionRange(lo, lo);\
         } else if (s > 0) {\
-            t.value = v.slice(0, s - 1) + v.slice(s);\
+            globalThis.__obscura_setFieldValue(t, 'value', v.slice(0, s - 1) + v.slice(s));\
             t.setSelectionRange(s - 1, s - 1);\
         }\
     }\
@@ -173,7 +173,7 @@ pub async fn handle(
                                 if (!target) return;\
                                 target.dispatchEvent(globalThis.__obscura_markTrusted(new KeyboardEvent('keypress', {bubbles:true,key:'Enter',code:'Enter'})));\
                                 if (target.localName === 'textarea') {\
-                                    target.value = (target.value || '') + '\\n';\
+                                    globalThis.__obscura_setFieldValue(target, 'value', (target.value || '') + '\\n');\
                                     target.dispatchEvent(globalThis.__obscura_markTrusted(new Event('input', {bubbles:true})));\
                                 } else {\
                                     var form = target.form || (target.closest && target.closest('form'));\