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/package.json

@@ -0,0 +1,39 @@
+{
+  "name": "@fusion/pi-claude-cli",
+  "version": "0.3.1",
+  "description": "Fusion vendored fork: pi coding-agent extension that routes LLM calls through the Claude Code CLI. Forked from rchern/pi-claude-cli (MIT). See UPSTREAM.md.",
+  "license": "MIT",
+  "private": true,
+  "type": "module",
+  "main": "index.ts",
+  "keywords": [
+    "pi-package"
+  ],
+  "pi": {
+    "extensions": [
+      "index.ts"
+    ]
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/Runfusion/Fusion",
+    "directory": "packages/pi-claude-cli"
+  },
+  "dependencies": {
+    "cross-spawn": "^7.0.6"
+  },
+  "peerDependencies": {
+    "@mariozechner/pi-ai": "*",
+    "@mariozechner/pi-coding-agent": "*"
+  },
+  "devDependencies": {
+    "@types/cross-spawn": "^6.0.6",
+    "@types/node": "^22.0.0",
+    "typescript": "^5.7.0",
+    "vitest": "^3.0.0"
+  },
+  "scripts": {
+    "test": "vitest run --reporter=dot",
+    "typecheck": "tsc --noEmit"
+  }
+}