Fix Edit/Save not applying to an already-connected External MCP server

ExternalMCPManager.reconfigure() only started brand-new clients — a
server ID that already had a client (in ANY state, including .crashed)
was silently skipped even when its settings had just changed. Editing a
server in Settings and clicking Save persisted correctly but never
reached the live connection, which just kept running with its old
(often broken) config until the next app launch. Rune hit this directly
editing Obsidian's URL/token after the toggle-fields bug corrupted it.

Added ExternalMCPServer: Equatable so reconfigure can detect a changed
config for a still-enabled server and restart it fresh (extracted the
restart-attempt-reset logic already used by retryClient into a shared
restartFresh helper).

oAI/Services/ExternalMCPModels.swift

@@ -14,7 +14,7 @@ nonisolated enum MCPTransportKind: String, Codable, Sendable, CaseIterable {
     case http
 }
 
-nonisolated struct ExternalMCPServer: Codable, Identifiable, Sendable {
+nonisolated struct ExternalMCPServer: Codable, Identifiable, Sendable, Equatable {
     var id: UUID
     var name: String
     var transportKind: MCPTransportKind