fix(web): only write settings on a real header edit; label rows by position (#1915)

Round-3 review follow-ups on #2038.

`buildHeaderSettingsPatch` treated the mere presence of stored headers as a
change, so saving an id or URL edit re-sent the modal's settings snapshot —
taken when it opened — and could overwrite a metadata or OAuth change made
in the settings form since. It now compares the submitted headers against
the stored ones and omits `settings` when they match, which is what makes
the PUT route preserve the node. Order counts as a difference: it is what
the form round-trips and what the user sees.

Row labels carried the key alone, so two rows sharing a key — mid-edit, or a
duplicate a server persisted — gave both rows' controls identical accessible
names, the thing the labelling exists to prevent. The row number is now
always part of the label rather than a blank-key fallback.

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

clients/web/src/components/groups/ServerSettingsModal/ServerSettingsModal.test.tsx

@@ -277,7 +277,9 @@ describe("ServerSettingsModal", () => {
     );
     await user.click(screen.getByRole("button", { name: "Custom Headers" }));
     await user.click(
-      screen.getByRole("button", { name: "Remove header, Authorization" }),
+      screen.getByRole("button", {
+        name: "Remove header, Authorization, row 1",
+      }),
     );
     expect(onSettingsChange).toHaveBeenCalledWith({
       ...initialSettings,
@@ -346,7 +348,9 @@ describe("ServerSettingsModal", () => {
     // Both the header and metadata rows have a remove button; each is named
     // for the row it belongs to, so no positional guess is needed.
     await user.click(
-      screen.getByRole("button", { name: "Remove metadata entry, userId" }),
+      screen.getByRole("button", {
+        name: "Remove metadata entry, userId, row 1",
+      }),
     );
     expect(onSettingsChange).toHaveBeenCalledWith({
       ...initialSettings,
@@ -767,7 +771,9 @@ describe("ServerSettingsModal", () => {
         screen.getByRole("button", { name: "Environment Variables" }),
       );
       await user.click(
-        screen.getByRole("button", { name: "Remove environment variable, A" }),
+        screen.getByRole("button", {
+          name: "Remove environment variable, A, row 1",
+        }),
       );
       expect(onSettingsChange).toHaveBeenCalledWith({
         ...emptySettings,