docs(settings): make AWS_REGION note deployment-agnostic

settings.example.json is consumed by two very different deployments:
the native workstation (where pi-env.zsh sources ~/.config/pi/.env — the
path is real and correct) AND the pi-devbox image, which bakes this file
as the settings.json seed at /opt/pi-toolkit/. In the container there is
no ~/.config/pi/.env: env comes from the compose env_file. The old
comment pointed only at the workstation path, which is stale/misleading
inside the container.

Reword to 'Must match your AWS_REGION' — accurate in both contexts,
without asserting a path that exists in only one. Comment-only change;
no keys touched. The other ~/.config/pi/.env references (install.sh,
README, AGENTS, pi-env.zsh) are workstation-correct and left as-is.

settings.example.json

@@ -1,6 +1,6 @@
 {
   "_comment": "Template for ~/.pi/agent/settings.json. Copy to that path and adjust for your region/account — this file is NOT symlinked by install.sh because pi rewrites settings.json at runtime (lastChangelogVersion bumps), which would dirty the repo. This template exists so a fresh machine can start pi without --model by copying + editing.",
-  "_comment_models": "The 'eu.' prefix on Bedrock model IDs is an inference-profile prefix tied to the AWS region. Must match AWS_REGION in ~/.config/pi/.env. For us-east use 'us.anthropic.*'; for bare Anthropic provider (non-Bedrock) use the raw 'anthropic:claude-*' IDs. Run `pi --list-models` to see what your credentials can actually invoke.",
+  "_comment_models": "The 'eu.' prefix on Bedrock model IDs is an inference-profile prefix tied to the AWS region. Must match your AWS_REGION. For us-east use 'us.anthropic.*'; for bare Anthropic provider (non-Bedrock) use the raw 'anthropic:claude-*' IDs. Run `pi --list-models` to see what your credentials can actually invoke.",
 
   "defaultProvider": "amazon-bedrock",
   "defaultModel": "eu.anthropic.claude-opus-4-8",