bridge the host pi config, with the credential by env only

The image ships pi with no provider and no preferences, so a sandboxed run
meant configuring the model twice. ai-sandbox now reads the host
~/.pi/agent/{models,settings}.json and rewrites them instead of copying them:
every provider apiKey becomes "$AI_API_TOKEN" (pi resolves an env reference
itself, so no value is written to disk), '!command' header values are dropped
rather than executed, settings that point into $HOME are dropped because that
path is not mounted, and auth.json / models-store.json / sessions / extensions
are never read.

The rewritten pair is seeded into /home/sandbox/.pi/agent at container start,
owned by uid 1000 and mode 600, and is treated as managed: a host change is
re-seeded, an edit made inside the sandbox is kept and reported, a deletion
takes the host version again.

The token follows the existing environment rules -- one variable, passed by
name through the 0600 env file, announced when auto-passed. A bridged run
whose token variable is unset or empty is refused instead of starting a pi
that cannot reach its model, and the bridge never widens the allowlist: it
warns with the exact --allow to add.

Docs and examples now use a self-hosted gateway (https://aipi.reeseapps.com)
instead of vendor API endpoints, since that is the only thing this tool is
used against. 391 assertions pass (make lint, ./tests/run.sh --e2e).

LLM-Generated: true

config/allow.example

@@ -10,11 +10,12 @@
 #   10.20.0.0/24      pinned subnet (default ports 80,443 unless :port given)
 #   [fd00::5]:8443    pinned ipv6
 
-api.anthropic.com
+aipi.reeseapps.com                               # your model gateway
 registry.npmjs.org
 
 # typical additions, by kind:
-# api.openai.com
+# another gateway or a LAN inference host:
+# gateway.internal:8443
 # github.com                                     # git push, if you also mount ~/.ssh
 # pypi.org
 # files.pythonhosted.org