feat: bump pi coding agent to 0.79.1 for Claude Fable 5 support

Update @earendil-works/pi-coding-agent and @earendil-works/pi-ai from
^0.78.0 to ^0.79.1 across cli, engine, and dashboard. This brings in
Claude Fable 5 (claude-fable-5) on the Anthropic and Amazon Bedrock
providers.

Fusion's model picker is registry-driven (/api/models -> pi ModelRegistry,
filtered by provider, not model id), so Fable surfaces automatically for
users with Anthropic or Claude CLI auth configured — no Fusion-side model
list change needed.

Verified: all core packages typecheck clean against 0.79.1; boot smoke
(fn --help, /api/health 200, clean shutdown) passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/engine/package.json

@@ -40,8 +40,8 @@
   "dependencies": {
     "@fusion/core": "workspace:*",
     "@fusion/pi-claude-cli": "workspace:*",
-    "@earendil-works/pi-ai": "^0.78.0",
-    "@earendil-works/pi-coding-agent": "^0.78.0",
+    "@earendil-works/pi-ai": "^0.79.1",
+    "@earendil-works/pi-coding-agent": "^0.79.1",
     "cron-parser": "^5.5.0",
     "esbuild": "^0.25.12",
     "node-pty": "npm:@homebridge/node-pty-prebuilt-multiarch@^0.13.1",