feat(FN-2978): add droid-cli package with provider registration and model d

This merge introduces a new `packages/droid-cli` package that bridges AI agent execution as a subprocess, including process management, event streaming, tool mapping, MCP configuration, and thinking-mode support. It also adds the `DroidCliProviderCard` dashboard UI component with onboarding flows an

Fusion-Task-Id: FN-2978

packages/droid-cli/README.md

@@ -0,0 +1,25 @@
+# @fusion/droid-cli
+
+First-party Fusion pi extension package that routes pi provider requests through the `droid` CLI subprocess using stream-json NDJSON.
+
+## Provider
+
+- Provider ID: `droid-cli`
+- Binary: `droid` (must be installed and authenticated on PATH)
+- Registration: package extension entrypoint in `index.ts`
+
+## Capabilities
+
+- Subprocess streaming bridge for text/thinking/tool events
+- Model auto-discovery from Droid CLI at provider startup with in-process caching
+- Session resume support (`--resume` / `--session-id`) to avoid replaying prior turns
+- MCP schema bridge for exposing pi custom tools as schema-only definitions
+- Tool mapping and break-early control so pi remains the tool executor
+- Thinking effort mapping from pi reasoning options to Droid CLI flags
+
+## Development
+
+```bash
+pnpm --filter @fusion/droid-cli test
+pnpm --filter @fusion/droid-cli exec tsc --noEmit
+```