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/lib/oauthResume.test.ts

@@ -80,7 +80,7 @@ describe("oauthResume", () => {
       tabUi: {
         Tools: {
           ...EMPTY_TOOLS_UI,
-          selectedToolName: "echo",
+          selectedToolKey: "0:echo",
           formValues: { message: "hi" },
         },
       },
@@ -96,7 +96,7 @@ describe("oauthResume", () => {
   it("builds and restores tab ui snapshots", () => {
     const toolsUi = {
       ...EMPTY_TOOLS_UI,
-      selectedToolName: "get_temp",
+      selectedToolKey: "1:get_temp",
       formValues: { city: "NYC" },
     };
     const tabUi = buildTabUiSnapshot({
@@ -186,7 +186,7 @@ describe("oauthResume", () => {
   it("applyOAuthResumeUi restores tab ui, active tab, and clears in-flight panels", () => {
     const toolsUi = {
       ...EMPTY_TOOLS_UI,
-      selectedToolName: "get_temp",
+      selectedToolKey: "1:get_temp",
       formValues: { city: "NYC" },
     };
     const snapshot: OAuthResumeSnapshot = {