ci: create GitHub Release after PyPI publish (#555)

Restores tag + GitHub Release creation that was previously handled by the
Speakeasy reusable workflow. Tag scheme matches what Speakeasy used
(v<version>). Release body is built from the latest entry in RELEASES.md
so the format matches v1.x / v2.x releases through v2.4.5.

PyPI publishing is atomic (no staging), so the release is created after
gh-action-pypi-publish succeeds. Adds contents: write to the workflow
permissions, required by gh release create.

Author: Nelson-PROIA

.github/workflows/sdk_publish_mistralai_sdk.yaml

@@ -1,6 +1,6 @@
 name: Publish MISTRALAI-SDK
 permissions:
-  contents: read
+  contents: write
   id-token: write
 "on":
   workflow_dispatch:
@@ -48,3 +48,46 @@ jobs:
           print-hash: true
           verbose: true
           skip-existing: true
+
+      - name: Create GitHub Release
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -euo pipefail
+
+          VERSION=$(awk -F\" '/^version[[:space:]]*=/ {print $2; exit}' pyproject.toml)
+          if [ -z "$VERSION" ]; then
+            echo "Could not read version from pyproject.toml" >&2
+            exit 1
+          fi
+          echo "Detected version: $VERSION"
+
+          TAG="v${VERSION}"
+          INVOKE_TIME=$(date -u '+%Y-%m-%d %H:%M:%S')
+
+          BODY_FILE=$(mktemp)
+          {
+            printf '# Generated by Speakeasy CLI\n\n'
+            if [ -f RELEASES.md ]; then
+              awk '/^## /{buf=""} {buf=buf $0 "\n"} END{printf "%s", buf}' RELEASES.md
+            fi
+            printf '\nPublishing Completed\n'
+          } > "$BODY_FILE"
+
+          # PEP 440 prerelease tokens: aN / bN / rcN / .devN / .postN-with-dev
+          PRERELEASE_FLAG=""
+          if [[ "$VERSION" =~ (a|b|rc|\.dev)[0-9]+ ]]; then
+            PRERELEASE_FLAG="--prerelease"
+          fi
+
+          if gh release view "$TAG" --repo "$GITHUB_REPOSITORY" >/dev/null 2>&1; then
+            echo "Release $TAG already exists, skipping."
+            exit 0
+          fi
+
+          gh release create "$TAG" \
+            --repo "$GITHUB_REPOSITORY" \
+            --target "$GITHUB_SHA" \
+            --title "python - ${TAG} - ${INVOKE_TIME}" \
+            --notes-file "$BODY_FILE" \
+            $PRERELEASE_FLAG