chore: update launchdarkly-server-sdk-ai to ^0.15.0 and fix CI Python version (#16)

## Summary

Bumps the `launchdarkly-server-sdk-ai` dependency from `^0.14.0` (which
resolves to `>=0.14.0, <0.15.0`) to `^0.15.0` (`>=0.15.0, <0.16.0`) to
track the latest release of the Python AI SDK.

No other dependency or code changes are included.

### Updates since last revision

Fixed CI failure by updating the Python version used in the CI workflow
from 3.8 to 3.10. The `pyproject.toml` already required `python =
"^3.10"`, so CI was broken before this PR as well. Also updated the
README to say "Python 3.10 or higher" to match the actual requirement.

## Review & Testing Checklist for Human

- [ ] Verify that `launchdarkly-server-sdk-ai` 0.15.0 is API-compatible
with the example code. **Note:** The examples currently import
`AIConfig` from `ldai.client`, which does not exist in 0.14.x *or*
0.15.x (it appears to have been renamed to `AICompletionConfig`). This
is a **pre-existing issue**, not introduced by this PR, but means the
examples are broken on both old and new versions.
- [ ] Confirm the CI Python version bump from 3.8 → 3.10 is correct (it
matches the existing `python = "^3.10"` constraint in `pyproject.toml`).
- [ ] Run `poetry install --all-extras && poetry run openai-example`
(with appropriate env vars) to confirm the examples work after fixing
the pre-existing import issue.

### Notes

- The `poetry.lock` file is in `.gitignore` for this repo, so no lock
file changes are included.
- The CI and README Python version fixes address a **pre-existing
mismatch** — `pyproject.toml` already required `^3.10` but CI used 3.8
and the README said 3.8.
- Link to Devin Session:
https://app.devin.ai/sessions/8b0a4069b434416dbaa05daac9bd26f9
- Requested by: @kinyoklion

Author: kinyoklion

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
         with:
-          python-version: 3.8
+          python-version: '3.10'
 
       - name: Install poetry
         uses: abatilo/actions-poetry@7b6d33e44b4f08d7021a1dee3c044e9c253d6439

README.md

@@ -4,7 +4,7 @@ We've built a simple console application that demonstrates how LaunchDarkly's SD
 
 Below, you'll find the build procedure. For more comprehensive instructions, you can visit your [Quickstart page](https://docs.launchdarkly.com/home/ai-configs/quickstart) or the [Python reference guide](https://docs.launchdarkly.com/sdk/ai/python).
 
-This demo requires Python 3.8 or higher.
+This demo requires Python 3.10 or higher.
 
 ## Build Instructions
 

pyproject.toml

@@ -20,7 +20,7 @@ direct-judge-example = 'examples.direct_judge_example:main'
 
 [tool.poetry.dependencies]
 python = "^3.10"
-launchdarkly-server-sdk-ai = "^0.14.0"
+launchdarkly-server-sdk-ai = "^0.15.0"
 launchdarkly-server-sdk-ai-langchain = "^0.3.0"
 launchdarkly-server-sdk-ai-openai = "^0.1.0"
 launchdarkly-observability = { version = ">=0.1.0", optional = true }