fix(backend): Make Jinja Error on TextFormatter as value error (#11236)

<!-- Clearly explain the need for these changes: -->

This PR converts Jinja2 TemplateError exceptions to ValueError in the
TextFormatter class to ensure proper error handling and HTTP status code
responses (400 instead of 500).

### Changes 🏗️

<!-- Concisely describe all of the changes made in this pull request:
-->

- Added import for `jinja2.exceptions.TemplateError` in
`backend/util/text.py:6`
- Wrapped template rendering in try-catch block in `format_string`
method (`backend/util/text.py:105-109`)
- Convert `TemplateError` to `ValueError` to ensure proper 400 HTTP
status code for client errors
- Added warning logging for template rendering errors before re-raising
as ValueError

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  <!-- Put your test plan: -->
- [x] Verified that invalid Jinja2 templates now raise ValueError
instead of TemplateError
  - [x] Confirmed that valid templates continue to work correctly
  - [x] Checked that warning logs are generated for template errors
  - [x] Validated that the exception chain is preserved with `from e`

#### For configuration changes:

- [x] `.env.default` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

autogpt_platform/backend/backend/util/text.py

@@ -3,6 +3,7 @@ import logging
 import bleach
 from bleach.css_sanitizer import CSSSanitizer
 from jinja2 import BaseLoader
+from jinja2.exceptions import TemplateError
 from jinja2.sandbox import SandboxedEnvironment
 from markupsafe import Markup
 
@@ -101,8 +102,11 @@ class TextFormatter:
 
     def format_string(self, template_str: str, values=None, **kwargs) -> str:
         """Regular template rendering with escaping"""
-        template = self.env.from_string(template_str)
-        return template.render(values or {}, **kwargs)
+        try:
+            template = self.env.from_string(template_str)
+            return template.render(values or {}, **kwargs)
+        except TemplateError as e:
+            raise ValueError(e) from e
 
     def format_email(
         self,