Add contract_risk analyzer template for contractual risk extraction

[DB API Builder (dbapibuilder)]

## Purpose
Adds a new `contract_risk.json` analyzer template for Azure AI Content Understanding to help users analyze commercial contracts. It extracts core party details (buyer/seller, dates, contract value) and identifies contractual risk points with severity, affected party, clause reference, and mitigation suggestions — enabling automated contract risk review at scale.

## Does this introduce a breaking change?

[ ] Yes
[x] No

## Pull Request Type

[ ] Bugfix
[x] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

## How to Test
* Get the code

git clone https://github.com/dbapibuilder/azure-ai-content-understanding-python
cd azure-ai-content-understanding-python
git checkout feature/add-contract-risk-analyzer
pip install -r requirements.txt

* Test the code

1. Configure your Azure AI Content Understanding endpoint and key in `.env`.
2. Open `notebooks/field_extraction.ipynb`.
3. Set the analyzer template path to `analyzer_templates/contract_risk.json`.
4. Run the notebook against a sample commercial contract (PDF or DOCX).
5. Confirm the notebook completes without errors and returns structured JSON output.

## What to Check
* `ContractType` is classified into one of: Sales, Service, Purchase, Supply, NDA, MSA, SOW, Lease, Employment, Other
* `OverallRiskLevel` returns one of: Low, Medium, High, Critical
* `RiskPoints` array items each contain: `RiskCategory`, `RiskTitle`, `RiskDescription`, `AffectedParty`, `Severity`, `ClauseReference`, `MitigationSuggestion`
* `KeyObligations` correctly identifies obligations and the responsible party
* `MissingOrAmbiguousTerms` surfaces vague or absent clauses
* Existing analyzer templates are unaffected

## Other Information
New analyzer template file: `analyzer_templates/contract_risk.json`

Fields introduced: `ContractTitle`, `ContractNumber`, `ContractType`, `BuyerCompanyName`, `SellerCompanyName`, `BuyerAddress`, `SellerAddress`, `EffectiveDate`, `ExecutionDate`, `ExpirationDate`, `AutoRenewal`, `Currency`, `ContractValue`, `PaymentTerms`, `GoverningLaw`, `TerminationNoticePeriod`, `LiabilityCap`, `OverallRiskLevel`, `RiskSummary`, `RiskPoints`, `KeyObligations`, `MissingOrAmbiguousTerms`

[DB API Builder (dbapibuilder)]

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