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/test/integration/server/web-server-config.test.ts

@@ -34,6 +34,9 @@ const baseConfig = (): WebServerConfig => ({
   authToken: "tok",
   dangerouslyOmitAuth: false,
   initialMcpConfig: null,
+  mcpConfigPath: undefined,
+  writable: true,
+  initialServers: null,
   storageDir: undefined,
   allowedOrigins: ["http://localhost:6274"],
   sandboxPort: 0,
@@ -202,6 +205,29 @@ describe("buildWebServerConfig", () => {
     );
   });
 
+  it("threads mcpConfigPath through and defaults it to undefined", () => {
+    expect(buildWebServerConfig().mcpConfigPath).toBeUndefined();
+    expect(
+      buildWebServerConfig({ mcpConfigPath: "/tmp/catalog/mcp.json" })
+        .mcpConfigPath,
+    ).toBe("/tmp/catalog/mcp.json");
+  });
+
+  it("defaults writable to true and initialServers to null", () => {
+    const cfg = buildWebServerConfig();
+    expect(cfg.writable).toBe(true);
+    expect(cfg.initialServers).toBeNull();
+  });
+
+  it("threads writable and initialServers when provided", () => {
+    const initialServers = {
+      mcpServers: { srv: { type: "stdio" as const, command: "node" } },
+    };
+    const cfg = buildWebServerConfig({ writable: false, initialServers });
+    expect(cfg.writable).toBe(false);
+    expect(cfg.initialServers).toBe(initialServers);
+  });
+
   it("preserves a stdio initialMcpConfig while applying shared env defaults", () => {
     process.env.CLIENT_PORT = "7000";
     const initialMcpConfig = {