Extensions UI: own Advertised Extensions section + 'Client Advertised Extensions' heading (#1748)

* Settings: move Advertised Extensions to its own accordion section (#1747)

The Advertised Extensions control (added in #1739) lived inside the Options
accordion panel, wedged between "Fetch Lists One Page at a Time" and "Network
Log Size". Promote it to its own top-level "Advertised Extensions" accordion
section (after Options), so the distinct concept — which extensions the
Inspector advertises to this server in its client capabilities — reads as its
own collapsible section.

- ServerSettingsForm: add "extensions" to ServerSettingsSection; move the
  checkbox group into a new Accordion.Item value="extensions". Its description
  moves up into the panel; no behavior change (still folds into
  settings.advertisedExtensions via onAdvertisedExtensionChange).
- ServerSettingsModal: add "extensions" to allSectionsFor so expand/collapse-all
  covers it.
- Tests: the toggle now lives under the new (collapsed-by-default) section, so
  the form tests render it expanded and the modal tests open it first.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* Connection Info: rename "Advertised Extensions" heading to "Client Advertised Extensions"

Disambiguates the client-side column from the adjacent "Server Extensions"
column and from the (separate) Server Settings "Advertised Extensions" section.
Label-only change; the value still renders clientCapabilities.extensions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* docs: refresh Connection Info screenshot for the renamed heading

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* docs: refresh #1747 proof screenshots (fresh capture)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

* Settings: add AdvertisedExtensions Storybook story (review)

Address the #1748 review's optional note: the new Advertised Extensions
accordion section had no story expanding it, so it wasn't documented in the
visual catalog (the default story expands only ['options']). Add an
AdvertisedExtensions story with expandedSections: ['extensions'] and a
per-server override, showing the default-on and toggled-off checkbox states.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNdjEPKLG637X8YmhDiEk5

---------

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

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

@@ -216,7 +216,9 @@ describe("ConnectionInfoContent", () => {
         protocolEra="legacy"
       />,
     );
-    expect(screen.getByText("Advertised Extensions")).toBeInTheDocument();
+    expect(
+      screen.getByText("Client Advertised Extensions"),
+    ).toBeInTheDocument();
     expect(
       screen.getByText(
         "io.modelcontextprotocol/tasks, io.modelcontextprotocol/ui",
@@ -234,7 +236,9 @@ describe("ConnectionInfoContent", () => {
       />,
     );
     expect(screen.getByText("Server Extensions")).toBeInTheDocument();
-    expect(screen.getByText("Advertised Extensions")).toBeInTheDocument();
+    expect(
+      screen.getByText("Client Advertised Extensions"),
+    ).toBeInTheDocument();
     // Exactly two em dashes: the two extension sections (the server version is
     // present in the fixture, so it does not em-dash).
     expect(screen.getAllByText("—")).toHaveLength(2);