fix(web): seed Edit-and-replay from what replay sends, name each JSON editor

Copilot's fourth pass, one inline plus two suppressed. All three were right.

- The modal presented the whole captured frame as editable, but replay does
  not re-send a frame: it dispatches through the typed InspectorClient
  methods, whose signatures have no room for `_meta` (a captured `tools/call`
  carries `_meta.progressToken`) or for any list-request key but `cursor`. So
  editing `_meta` and pressing Send transmitted something other than what was
  on screen. `replayableParams` now projects the frame down to what the
  dispatcher actually reads, the modal seeds from that, and it names what was
  left out rather than leaving the difference to be discovered. The projection
  lives beside the dispatch switch because the two are halves of one contract.

- `ContentViewer` gains `jsonLabel`, so a read-only JSON editor can say what
  it holds. Every one of them announced "JSON content", and an expanded
  Protocol entry has two while the list has many pairs — leaving a screen
  reader with indistinguishable textboxes and only the visible headings to
  tell them apart. Protocol entries now name theirs per method and direction,
  Network entries per request/response body.

- `isJsonDocument` became `formatJsonDocument`, returning the formatted text
  instead of a boolean. The heuristic path parsed the payload to decide and
  then parsed it again to render; Protocol and Network hand over serialized
  bodies as untyped text and are not virtualized, so a long history paid twice
  per payload per render.

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/components/groups/EditReplayModal/EditReplayModal.test.tsx

@@ -98,6 +98,44 @@ describe("EditReplayModal", () => {
     expect(screen.getByText(/Numbers must be finite/)).toBeInTheDocument();
   });
 
+  // Replay dispatches through the typed client methods, so a param they have no
+  // room for is dropped. Saying which, rather than seeding it into the editor,
+  // is what keeps the modal from inviting an edit that Send discards.
+  it("names the params replay cannot re-send", () => {
+    renderWithMantine(
+      <EditReplayModal
+        {...baseProps}
+        params={{ name: "echo" }}
+        droppedParamKeys={["_meta"]}
+      />,
+    );
+    expect(screen.getByText(/`_meta` is not re-sent/)).toBeInTheDocument();
+  });
+
+  it("says nothing when every param survives", () => {
+    renderWithMantine(
+      <EditReplayModal
+        {...baseProps}
+        params={{ name: "echo" }}
+        droppedParamKeys={[]}
+      />,
+    );
+    expect(screen.queryByText(/not re-sent/)).toBeNull();
+  });
+
+  it("agrees with its verb for several dropped params", () => {
+    renderWithMantine(
+      <EditReplayModal
+        {...baseProps}
+        params={{ cursor: "abc" }}
+        droppedParamKeys={["_meta", "extra"]}
+      />,
+    );
+    expect(
+      screen.getByText(/`_meta`, `extra` are not re-sent/),
+    ).toBeInTheDocument();
+  });
+
   it("closes without sending when cancelled", async () => {
     const user = userEvent.setup();
     const onSend = vi.fn();