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/components/groups/ServerListControls/ServerListControls.tsx

@@ -11,6 +11,8 @@ export interface ServerListControlsProps extends AddServerMenuProps {
   onToggleList: () => void;
   /** Download the current server list as a canonical `mcp.json` file. */
   onExport: () => void;
+  /** When false (read-only session), the Add menu is hidden. Defaults to true. */
+  writable?: boolean;
 }
 
 export function ServerListControls({
@@ -21,6 +23,7 @@ export function ServerListControls({
   onImportConfig,
   onImportServerJson,
   onExport,
+  writable = true,
 }: ServerListControlsProps) {
   return (
     <Group justify="flex-end">
@@ -30,11 +33,13 @@ export function ServerListControls({
       <Button variant="default" onClick={onExport} disabled={serverCount === 0}>
         Export
       </Button>
-      <ServerAddMenu
-        onAddManually={onAddManually}
-        onImportConfig={onImportConfig}
-        onImportServerJson={onImportServerJson}
-      />
+      {writable && (
+        <ServerAddMenu
+          onAddManually={onAddManually}
+          onImportConfig={onImportConfig}
+          onImportServerJson={onImportServerJson}
+        />
+      )}
     </Group>
   );
 }