fix(web): key tool selection by row identity, not name

#1961 keyed the sidebar's React children by source position, but everything
downstream still identified a tool by `tool.name`. With a `tools/list` that
repeats a name, both copies highlighted at once, the click guard made the
other copy a no-op, and `tools.find((t) => t.name === …)` always resolved to
the first — so a later copy rendered but could never be opened.

Thread the row key through selection instead:

- `utils/toolUtils.ts` now owns `toolRowKey` (moved out of ToolControls) and
  adds `findToolByRowKey`, which compares computed keys rather than parsing
  one so the two can't drift.
- `ToolControls`: `selectedName` → `selectedKey`; the highlight and the click
  guard compare keys, and `onSelectTool` emits the row key.
- `ToolsScreen`: `ToolsUiState.selectedToolName` → `selectedToolKey`, with
  both lookups going through `findToolByRowKey`. Renamed through
  `screenUiState.ts` and `App.tsx`'s `onToolsUiChange`.

`onCallTool` still sends `selectedTool.name` — the duplicated name is the
genuine wire identity; only the UI identity needed to be unique.

Also prefixes the excluded (SEP-2243) rows' keys: they render into the same
`Stack` as the list rows but index within their own list, so an excluded tool
sharing a name and index with a listed one collided in the key space.

Closes #2001

Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/App.tsx

@@ -3160,17 +3160,17 @@ function App() {
   // drops the previous tool's result — the result panel renders `toolCallState`
   // regardless of selection, so without this a stale result would linger under
   // the newly-selected tool (which has no result of its own yet). Search and
-  // form edits keep `selectedToolName` unchanged, so they leave the result be.
-  // Depends on `selectedToolName` only (not the whole `toolsUi`), so a search
+  // form edits keep `selectedToolKey` unchanged, so they leave the result be.
+  // Depends on `selectedToolKey` only (not the whole `toolsUi`), so a search
   // keystroke doesn't churn the callback identity.
   const onToolsUiChange = useCallback(
     (next: ToolsUiState) => {
-      if (next.selectedToolName !== toolsUi.selectedToolName) {
+      if (next.selectedToolKey !== toolsUi.selectedToolKey) {
         setToolCallState(undefined);
       }
       setToolsUi(next);
     },
-    [toolsUi.selectedToolName],
+    [toolsUi.selectedToolKey],
   );
 
   // --- MCP Apps handlers. Unlike onCallTool (which feeds the Tools panel),