feat(studio): MCP-clients editor + federated entry rendering (v0.22.0)

The viral-bridge story now has a UI surface. Settings →
MCP Clients lists every configured server, shows last-
discovery health (green dot + tool count, red dot + error
kind), and offers Add / Remove / Refresh.

Add-server dialog: name (no dots), endpoint, optional
api_key_env, optional notes. On submit the hub persists +
re-runs discovery in one round-trip; the Store fills with
synthetic `mcp.<name>.<tool>` entries the operator can see
immediately.

StoreItem now carries `kind` and `provider`. Federated
entries route through a bridge — no install bundle to
download — and Studio's install button renders accordingly
(via the existing "Not installable" path; the Phase-2
follow-up adds an explicit "Configure bridge" call-to-action).

Settings dialog grew to 520×640 with a SingleChildScrollView
so the additional panels don't crowd. Channel pill, system-AI
panel, MCP-clients panel all coexist without a redesign.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

pubspec.yaml

@@ -1,7 +1,7 @@
 name: fai_studio
 description: "F∆I Studio — desktop GUI for the F∆I hub"
 publish_to: 'none'
-version: 0.21.0
+version: 0.22.0
 
 environment:
   sdk: ^3.11.0-200.1.beta