Update web preview docs to use 127.0.0.1 instead of 0.0.0.0 (#1178)

Updates the web preview documentation to use `127.0.0.1` (localhost)
instead of `0.0.0.0` for the host binding.

## Changes Made
- Updated configuration section to recommend `127.0.0.1` as the
appropriate host
- Changed Django example from `0.0.0.0:8000` to `127.0.0.1:3000`
- Updated Rails example from `-b 0.0.0.0` to `-b 127.0.0.1 -p 3000`
- Maintains the port 3000 requirement as specified in the warning
section

This change ensures users bind their development servers to localhost
rather than all interfaces, which is more secure and appropriate for
local development.

---

[💻 View my work](https://codegen.com/agent/trace/61566) • [🚫 Ban all
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@kopekC • 💬 Initiated in
[#agi-test](https://thecodegen.slack.com/archives/C08DPPSL1CG/p1753463343125049?thread_ts=1753463343.125049&cid=C08DPPSL1CG)
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Co-authored-by: codegen-sh[bot] <131295404+codegen-sh[bot]@users.noreply.github.com>

Author: codegen-sh[bot]

docs/sandboxes/web-preview.mdx

@@ -23,7 +23,7 @@ A "View Web Preview" button appears on the agent trace page once the server star
 
 You configure Web Preview commands in a manner similar to Setup Commands, likely within the same repository settings area (e.g., `https://codegen.com/{your_org}/{repo_name}/settings/web-preview`).
 
-You'll provide the command(s) necessary to start your development server. Ensure that your server is configured to listen on an appropriate host (often `0.0.0.0`) and a predictable port that Codegen can then expose.
+You'll provide the command(s) necessary to start your development server. Ensure that your server is configured to listen on an appropriate host (often `127.0.0.1`) and a predictable port that Codegen can then expose.
 
 <Warning>
   The web server started for Web Preview **MUST** listen on port 3000. Codegen
@@ -42,12 +42,12 @@ npm run dev
 
 ```bash
 # For a Python/Django project
-python manage.py runserver 0.0.0.0:8000
+python manage.py runserver 127.0.0.1:3000
 ```
 
 ```bash
 # For a Ruby on Rails project
-bundle exec rails server -b 0.0.0.0
+bundle exec rails server -b 127.0.0.1 -p 3000
 ```
 
 <Tip>