feat(web): catalog vs read-only session launch model + apply --header (#1481, #1483) (#1496)

* feat(web): catalog vs read-only session launch model + apply --header (#1481, #1483)

Per specification/v2_catalog_launch_config.md, `mcp-inspector --web` now selects
the backend's server-list source and a session-wide writability, instead of
seeding an inert `initialMcpConfig` the UI never read:

- `--catalog <path>` (and `MCP_CATALOG_PATH`) → active WRITABLE catalog
  (seed/CRUD/watch), like the default catalog.
- `--config <path>` → READ-ONLY session file: served in the UI but never
  written, seeded, or plaintext-secret-migrated — safe to point at a foreign
  config (e.g. claude_desktop_config.json).
- ad-hoc `--server-url`/command (+ `--header`) → one server held IN MEMORY
  (no file written); `--header` is lifted onto the entry so the seeded
  connection actually uses it (closes the #1483 warn-only no-op).
- nothing → default catalog (writable), unchanged.

Backend (`createRemoteApp`): new `writable` + `initialServers` options. GET
/api/servers branches three ways (in-memory / read-only file with no
seed+no migrate / writable catalog); the four mutating routes return 403 when
read-only; `/api/config` carries `writable`; the file watcher is skipped for
in-memory sessions. `--catalog`/`--config` are mutually exclusive and neither
combines with an ad-hoc target or `--header`; `--header` requires an ad-hoc
HTTP/SSE server (clear errors otherwise — no silent no-op).

UI: `useServerListWritable` reads `writable` from /api/config; the Servers
screen hides add/edit/clone/remove/reorder/settings and shows a read-only
banner when false. All new props default to writable=true (back-compatible).

Docs: spec gaps G2/G3/G4 updated; launcher README documents the flags.

Verified end-to-end against the built launcher: --config (writable:false,
file byte-stable, mutations 403), ad-hoc --header (in-memory, header lifted),
and --catalog (writable:true, POST persists).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* refactor(web): address review — Mantine <Code> in read-only banner, clarify watcher comment

- Replace raw <code> with Mantine <Code> in the read-only-session Alert
  (repo convention: prefer Mantine primitives over raw HTML).
- Add a comment near `watchable` clarifying that a read-only `--config` file
  is still watched on purpose (read-only blocks UI writes, not external
  observation; `writable` does not gate watching).

Deferred (per reviewer): consolidating useSandboxUrl + useServerListWritable
into one useConfig hook to avoid the duplicate /api/config fetch — optional
follow-up. The redundant ad-hoc header type-guard is kept as defensive.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/App.tsx

@@ -78,6 +78,7 @@ import { useResourceSubscriptions } from "@inspector/core/react/useResourceSubsc
 import { useMessageLog } from "@inspector/core/react/useMessageLog.js";
 import { useFetchRequestLog } from "@inspector/core/react/useFetchRequestLog.js";
 import { useSandboxUrl } from "@inspector/core/react/useSandboxUrl.js";
+import { useServerListWritable } from "@inspector/core/react/useServerListWritable.js";
 import { usePendingClientRequests } from "@inspector/core/react/usePendingClientRequests.js";
 import { InspectorView } from "./components/views/InspectorView/InspectorView";
 import type {
@@ -537,11 +538,16 @@ function App() {
   // the active client's underlying SDK client so the running view can call the
   // server, and reads the tool's UI resource into the sandbox on handshake.
   const appRendererRef = useRef<AppRendererHandle>(null);
+  const configBaseUrl =
+    typeof window !== "undefined" ? window.location.origin : "http://localhost";
   const { sandboxUrl } = useSandboxUrl({
-    baseUrl:
-      typeof window !== "undefined"
-        ? window.location.origin
-        : "http://localhost",
+    baseUrl: configBaseUrl,
+    authToken: getAuthToken(),
+  });
+  // Read-only sessions (launched with `--config` or an ad-hoc server) hide
+  // catalog CRUD; the default catalog and `--catalog` stay writable.
+  const { writable: serverListWritable } = useServerListWritable({
+    baseUrl: configBaseUrl,
     authToken: getAuthToken(),
   });
   const sandboxBridgeFactory = useMemo(
@@ -2353,6 +2359,7 @@ function App() {
     <>
       <InspectorView
         servers={servers}
+        serverListWritable={serverListWritable}
         activeServer={activeServerId}
         connectionStatus={connectionStatus}
         initializeResult={initializeResult}