Fix show_toolbar_with_docker on runtimes with unrelated host address

[Sanjays2402]

Description

show_toolbar_with_docker derives the Docker host address by resolving
host.docker.internal and replacing the last segment with .1. On OrbStack
that name resolves to 0.250.250.254, which is outside the container network,
so the derived address never matches REMOTE_ADDR and the toolbar stays
hidden. When that probe does not match, the host address is now derived from
the container's own addresses instead.

Fixes #2419

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

AI/LLM Usage

• This PR includes code generated with the help of an AI/LLM

[tim-schilling]

I tweaked the solution to be more amenable to follow-up docker tests. If this new check fails, it shouldn't automatically return false. It ideally should fall through to the last return false statement.

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
debug_toolbar
middleware.py					45, 48, 63, 77-81
Project Total

This report was generated by python-coverage-comment-action

[tim-schilling]

Can you round out the tests to have coverage of the missing lines identified here: #2422 (comment)?

[tim-schilling]

Let's also update the documentation warning around docker with a note to include something like:

When the Docker host lookup fails, the show_toolbar_with_docker callback guesses the host's address from the container's own network. If run outside a container that guess resolve to another machine on your network, granting it access to the toolbar's data. The show_toolbar_with_docker callback should only be used inside a container.

[Sanjays2402]

Added that note to the Docker warning in docs/installation.rst (64ad00a), wording close to yours, just softened "resolve" to "can resolve":

When the Docker host lookup fails, the show_toolbar_with_docker callback guesses the host's address from the container's own network. If run outside a container that guess can resolve to another machine on your network, granting it access to the toolbar's data. The show_toolbar_with_docker callback should only be used inside a container.

Thanks for the fall-through rework, that reads better than the nested version I had.

[tim-schilling]

As I went to merge it I got cold-feet that someone could use this improperly. However, the check on DEBUG is solid, so not super worried about that, but I was a little worried someone may copy it without understand the implications. So I added an extra comment to explain what it's doing and where the risk would be if it were misused. Thank you @Sanjays2402 for this!

[alastair]

Thank you @tim-schilling and @Sanjays2402!