fix(extensions): always prefer vendored @fusion/pi-claude-cli over external installs

When users have an external pi-claude-cli (e.g. a global `npm install -g
pi-claude-cli`, or `npm:pi-claude-cli` in ~/.pi/agent/settings.json packages),
pi's extension discovery loaded the upstream copy and shadowed our fork. The
upstream has a once-and-lock MCP-config bug that throws "Extension runtime not
initialized" during early streamSimple calls and never recovers.

Adds reconcileClaudeCliPaths in @fusion/core, used by both the daemon's
extension assembly and the engine's per-session registerExtensionProviders, to
drop any path with a `pi-claude-cli` segment that isn't our vendored fork and
prepend the vendored path. Engine resolves the fork via require.resolve and
gracefully no-ops when it isn't reachable (e.g. embedded standalone usage).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/engine/package.json

@@ -36,6 +36,7 @@
   },
   "dependencies": {
     "@fusion/core": "workspace:*",
+    "@fusion/pi-claude-cli": "workspace:*",
     "@mariozechner/pi-ai": "^0.70.0",
     "@mariozechner/pi-coding-agent": "^0.70.0",
     "typebox": "^1.0.0",