Replace remaining stringly-typed MCP scope and settings file references

[bguidolim]

Context

PR #234's /simplify review added Constants.MCPScope.user and updated the files changed by that PR. However, there are remaining usages:

MCP scope strings

• ConfigurationDiscovery.swift:159 — scope: "user"
• ConfigurationDiscovery.swift:170 — scope: "local"
• Component.swift:131 — doc comment references "local", "project", "user" as bare strings

Settings file name

• ProjectSyncStrategy.swift:154 — hardcoded "settings.local.json" in error message (should use scope.settingsPath.lastPathComponent)

Proposed Fix

1. Use Constants.MCPScope.user / Constants.MCPScope.local in ConfigurationDiscovery.swift
2. Replace hardcoded settings file name with scope.settingsPath.lastPathComponent
3. Consider adding Constants.MCPScope.project and Constants.MCPScope.local if not already covered