Add AWS_BEDROCK_FORCE_CACHE=1 environment variable support. When the
model ID doesn't contain a recognizable Claude model name, users can
set this variable to force cache point injection.
When running inside a sandbox (e.g., bubblewrap) that blocks access
to the tmux socket, the tmux query hangs and times out, returning
undefined. Previously this was treated as "extended-keys is off",
showing a false warning. Now we skip the warning when the tmux server
can't be reached.