fix(cc-config): MCP scope was inverted — expose user/local, not user/project

readMcpServers only ever parses ~/.claude.json (top-level = user scope,
projects[<root>] = the panel's "projectScoped" bucket, which the CLI itself
calls `local`). The previous user/project scope choice was the exact
inverse: `--scope project` writes .mcp.json, which readMcpServers never
reads (a successful add would vanish), and every "projectScoped" row was
actually `local`, so Remove sent a scope the CLI could never match.

- cc-mcp-cli.js: MCP_SCOPES -> ["user", "local"]; drop the local
  mutationQueue/serialize in favor of cc-plugin-cli.js's exported one, so a
  plugin install and an MCP add can't spawn `claude` concurrently; drop the
  String(v) coercion in env/header flags (a wrong-typed value is now a 400,
  not a written "[object Object]"); assertEmbeddedValue allows empty strings
  (a legitimate empty stdio arg was previously a 400).
- cc-plugin-cli.js: export `serialize` for reuse.
- CcConfig.tsx: CcMcpScope narrowed to user/local; the projectScoped bucket's
  McpCard now sends scope="local"; rows sourced from
  ~/.claude/settings.json (no CLI scope addresses them) no longer render a
  Remove button. Cleaned up i18n keys my own earlier change made dead
  (explain.mcp.addCmd/remove/removeButton) and gave the scope <select> its
  own short option labels instead of reusing full-sentence section headings.

client/src/pages/CcConfig.tsx

@@ -1903,8 +1903,8 @@ function McpPanel({
             aria-label={t("mcp.scope")}
             className="h-8 bg-surface-1 border border-border rounded px-2 text-[12px] text-fg-primary focus:outline-none focus:ring-1 focus:ring-accent/40"
           >
-            <option value="user">{t("mcp.userScope")}</option>
-            <option value="project">{t("mcp.projectScope")}</option>
+            <option value="user">{t("mcp.scopeUser")}</option>
+            <option value="local">{t("mcp.scopeLocal")}</option>
           </select>
           <div className="flex rounded-md border border-border overflow-hidden">
             {(["stdio", "http"] as const).map((k) => (
@@ -1994,7 +1994,7 @@ function McpPanel({
               <McpCard
                 key={`p:${s.name}:${s.source}`}
                 server={s}
-                scope="project"
+                scope="local"
                 run={run}
                 busy={busy}
                 t={t}
@@ -2022,6 +2022,10 @@ function McpCard({
 }) {
   const [confirmRemove, setConfirmRemove] = useState(false);
   const busyId = `${scope}:${server.name}`;
+  // Entries from ~/.claude/settings.json have no CLI scope that addresses
+  // them (`claude mcp remove` only ever touches ~/.claude.json / .mcp.json)
+  // — a Remove button here would look live and never work.
+  const removable = server.source !== "~/.claude/settings.json";
   return (
     <div className="rounded-lg border border-border bg-surface-2 px-4 py-3">
       <div className="flex items-center gap-2 flex-wrap">
@@ -2063,29 +2067,33 @@ function McpCard({
         )}
       </div>
       <div className="mt-3">
-        <ActionButton
-          icon={Trash2}
-          danger
-          disabled={busy === busyId}
-          onClick={() => {
-            if (!confirmRemove) {
-              setConfirmRemove(true);
-              return;
-            }
-            setConfirmRemove(false);
-            void run(
-              busyId,
-              () => api.ccConfig.mcpRemove(server.name, scope),
-              t("manage.mcpRemoved", { name: server.name })
-            );
-          }}
-        >
-          {busy === busyId
-            ? t("manage.working")
-            : confirmRemove
-              ? t("manage.confirmRemove")
-              : t("manage.remove")}
-        </ActionButton>
+        {removable ? (
+          <ActionButton
+            icon={Trash2}
+            danger
+            disabled={busy === busyId}
+            onClick={() => {
+              if (!confirmRemove) {
+                setConfirmRemove(true);
+                return;
+              }
+              setConfirmRemove(false);
+              void run(
+                busyId,
+                () => api.ccConfig.mcpRemove(server.name, scope),
+                t("manage.mcpRemoved", { name: server.name })
+              );
+            }}
+          >
+            {busy === busyId
+              ? t("manage.working")
+              : confirmRemove
+                ? t("manage.confirmRemove")
+                : t("manage.remove")}
+          </ActionButton>
+        ) : (
+          <p className="text-[10px] text-fg-muted">{t("mcp.notRemovable")}</p>
+        )}
       </div>
     </div>
   );