Patch CVEs in engine Python dependencies (#6804)

# Description of Changes

- Patch CVEs in engine Python dependencies (43 alerts): `starlette`
1.3.1, `cryptography` 49.0.0, `pyjwt` 2.13.0, `urllib3` 2.7.0, `aiohttp`
3.14.1, `python-multipart` 0.0.32, `langchain-core` 1.4.8, `langsmith`
0.9.1, `authlib` 1.7.2, `requests` 2.34.2, `idna` 3.18, `pytest` 9.1.1,
`pygments` 2.20.0, `pydantic-settings` 2.14.2
- Cap `pydantic-ai` `<2.0.0` and bump to 1.107.0 (1.99.0 patches
CVE-2026-46678; 2.0 is a separate major migration)

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs (if functionality has heavily
changed)
- [ ] I have read the section Add New Translation Tags (for new
translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached

### Testing (if applicable)

- [ ] I have run `task check` to verify linters, typechecks, and tests
pass
- [ ] I have tested my changes locally

engine/pyproject.toml

@@ -8,8 +8,9 @@ dependencies = [
     "pgvector>=0.3.6",
     "psycopg[binary,pool]>=3.2",
     "pydantic>=2.0.0",
-    "pydantic-ai>=1.67.0",
-    "pydantic-ai-slim[voyageai]>=1.67.0",
+    # <2 cap: 1.99.0 patches CVE-2026-46678; 2.0 is an untested major migration
+    "pydantic-ai>=1.99.0,<2.0.0",
+    "pydantic-ai-slim[voyageai]>=1.99.0,<2.0.0",
     "pydantic-settings>=2.0.0",
     "python-dotenv>=1.2.1",
     "sqlite-vec>=0.1.6",