v0.9.1 — activate Patchright fallback + learning host-key fix

Activate the Patchright fallback and align the self-learning host key.

• Patchright activated (engine/templates/package.json): added patchright (^1.61.1). The real-Chrome template already preferred require('patchright') but the package was never declared, so it always fell back to playwright-extra+stealth. Patchright is a Playwright-API-compatible drop-in that patches the CDP Runtime.enable (console-attach) leak that modern Cloudflare/DataDome-class detection keys on. Verified end-to-end (automation:patchright, HTTP 200, real HTML). Falls back to playwright-extra+stealth → plain playwright when absent (all on channel:'chrome').
• Learning host-key fix (engine/learning.py): key_for used netloc (kept port + userinfo) while the session pool and browser profile dir key on hostname. Switched to hostname so learned route, warm session, and profile share one key.
• Docs: install instructions updated to local engine/templates npm install with npx patchright install chrome.

Full engine regression 59/59; bias_check clean.