feat(web): use the Ace JSON editor everywhere, and restore the raw-JSON toggle

Extracts the Ace integration #2094 carried inline into a shared
`elements/JsonEditor`, and renders it on every surface where the web
client types or displays JSON.

The element is deliberately text in, text out. The two editing contracts
above it disagree about what an unparseable draft means — JsonObjectInput
keeps the last valid object and says nothing to its parent, SchemaJsonField
reports `undefined` and blocks submission (#2020) — so parsing, and the
draft/value split that goes with it, stays with each caller.

Surfaces: SchemaJsonField (inherited by all four SchemaForm consumers), a
new "Edit as JSON" switch for the whole arguments object, the server.json
File Contents box, the raw JSON-RPC request box, ContentViewer's JSON
branch (read-only, inherited by its eleven consumers), and a new "Edit and
replay" modal on a Protocol entry.

Ace read-only replaces the CodeHighlight JSON path and the Prism `json`
grammar loader is dropped: folding, not colorization, is what it adds, and
two highlighters for one language drift. `wrap={false}` callers and untyped
text that only looks like JSON keep the plain renderer.

Closes #2151

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UL9retfvAXRgvi6EWk4SY4
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/App.css

@@ -615,3 +615,10 @@ body.resizing-col {
 .ace_editor.ace-github-dark .ace_gutter {
   color: var(--inspector-code-gutter-text);
 }
+
+/* A read-only Ace editor still paints a caret, which reads as an editable field
+   whose keystrokes are being swallowed. `readOnly` has no option that removes
+   it, so — like the gutter above — it can only be reached by selector. */
+.ace_editor.json-editor-readonly .ace_cursor {
+  display: none;
+}