Fix: Revert accidental case-sensitive changes

Reverted unintended case changes that occurred during the global rename:
- GitHub Actions: Changed ANTHROPIC_API_KEY back to anthropic_api_key in workflow files
- Python function: Changed ANTHROPIC_API_KEY parameter back to anthropic_api_key in ContextualVectorDB class

These changes maintain consistency with Python naming conventions (snake_case) and
the original GitHub Actions workflow configuration.

🤖 Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/claude-link-review.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Run Claude Link Review
         uses: anthropics/claude-code-action@v1
         with:
-          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
           prompt: "/link-review"
           claude_args: |

.github/workflows/claude-model-check.yml

@@ -24,7 +24,7 @@ jobs:
       - name: Claude Model Validation
         uses: anthropics/claude-code-action@v1
         with:
-          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
           prompt: "/model-check"
           claude_args: |

.github/workflows/claude-notebook-review.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Run Claude Notebook Review
         uses: anthropics/claude-code-action@v1
         with:
-          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
           prompt: "/notebook-review"
           claude_args: |

.github/workflows/notebook-quality.yml

@@ -57,7 +57,7 @@ jobs:
         if: github.event_name == 'pull_request' && steps.validate.outputs.has_issues == 'true'
         uses: anthropics/claude-code-action@v1
         with:
-          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           github_token: ${{ secrets.GITHUB_TOKEN }}
           prompt: |
             The notebook validation found these issues:
@@ -88,7 +88,7 @@ jobs:
           github.event.pull_request.author_association == 'MEMBER' ||
           github.event.pull_request.author_association == 'OWNER'
         env:
-          ANTHROPIC_API_KEY: ${{ secrets.ANTHROPIC_API_KEY }}
+          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
         run: |
           mkdir -p test_outputs
           for notebook in $(find . -name "*.ipynb" -not -path "*/.*" -not -path "*/test_outputs/*"); do