feat: add "Anthropic — via Claude CLI" as a first-class provider

Replaces the stray useClaudeCli settings checkbox + onboarding question
with a proper provider-card UX. The card lives next to OAuth + API-key
cards in onboarding and settings, with Enable/Disable + Test actions.

Backend:
 - Vendors rchern/pi-claude-cli@0.3.1 as packages/pi-claude-cli
   (MIT, attribution in UPSTREAM.md). Lets us bump peer-dep on
   pi-coding-agent in lockstep with Fusion (upstream pinned ^0.52.0
   vs ours ^0.62.0) and fix bugs without waiting on upstream.
 - Adds @fusion/pi-claude-cli as a workspace dep of @runfusion/fusion
   so users don't have to `npm install -g pi-claude-cli` manually.
 - serve/daemon/dashboard conditionally load the extension via
   discoverAndLoadExtensions() when GlobalSettings.useClaudeCli is on;
   no side-effects on user ~/.fusion/agent/settings.json.
 - New GET /api/providers/claude-cli/status: claude --version probe
   + toggle state + cached extension resolution.
 - New POST /api/auth/claude-cli: flips useClaudeCli, refuses if the
   claude binary is missing, fires the existing skill-backfill hook.
 - /api/auth/status now injects a synthetic {id:"claude-cli", type:"cli"}
   provider entry so onboarding + settings see a consistent list.

Frontend:
 - New ClaudeCliProviderCard component shared between ModelOnboardingModal
   and SettingsModal's Authentication section.
 - New AuthProvider.type = "cli" variant.
 - Removed the old "Route AI calls through the Claude CLI" checkbox from
   Global Models settings and the opt-in step from the onboarding wizard.
 - ProviderIcon gets a composite Anthropic-mark-plus-terminal glyph for
   the claude-cli provider id.

Tests:
 - 8 unit tests for extension resolution (@fusion/pi-claude-cli is
   workspace-linked so these run in-tree).
 - 2 unit tests for the binary probe.
 - Existing /auth/status tests filter out the new synthetic entry so
   they keep asserting structural OAuth/API-key behavior in isolation.
 - The vendored package's own 296 tests still pass unchanged.

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

packages/pi-claude-cli/README.md

@@ -0,0 +1,40 @@
+# pi-claude-cli
+
+A [pi](https://github.com/mariozechner/pi-coding-agent) extension that routes LLM calls through the [Claude Code CLI](https://docs.anthropic.com/en/docs/claude-code) as a subprocess. Use your Claude Pro/Max subscription as the LLM backend — no API key, no separate billing.
+
+## How it works
+
+The extension registers as a custom pi provider exposing all Claude models. Each request spawns a `claude -p` subprocess using the stream-json wire protocol, with `--resume` on follow-up turns to reuse the CLI's session state instead of replaying full history. Claude proposes tool calls, pi executes them natively. Custom pi tools are exposed to Claude via a schema-only MCP server.
+
+## Requirements
+
+- [Claude Code CLI](https://docs.anthropic.com/en/docs/claude-code) installed and authenticated (`claude` on PATH)
+- A Claude Pro or Max subscription
+- [pi](https://github.com/mariozechner/pi-coding-agent) or [GSD](https://github.com/gsd-build/gsd-2)
+
+## Installation
+
+Add to `~/.gsd/agent/settings.json`:
+
+```json
+{
+  "packages": ["npm:pi-claude-cli"]
+}
+```
+
+Then select a Claude model via `/model` in the interactive UI. All Claude models appear under the `pi-claude-cli` provider.
+
+## Features
+
+- Streams text, thinking, and tool call tokens in real-time
+- Maps tool names and arguments bidirectionally between Claude and pi
+- Exposes custom pi tools to Claude via MCP (schema-only, no execution)
+- Break-early pattern prevents Claude CLI from auto-executing tools
+- Session resume via `--resume` eliminates history replay on follow-up turns
+- Configurable thinking effort with elevated budgets for Opus models
+- Cross-platform subprocess management (Windows, macOS, Linux)
+- Inactivity timeout and process registry for cleanup
+
+## License
+
+MIT