Add CI validation workflow and collection lifecycle

ai/select-algorithm-dotnet/README.md

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+# Select Algorithm - .NET (C#)
+
+Demonstrates three vector index algorithms available in Azure DocumentDB (vCore):
+
+| Algorithm | Best For | Cluster Tier | Key Parameters |
+|-----------|----------|--------------|----------------|
+| **IVF** | < 10,000 documents | M10+ | `numLists` |
+| **HNSW** | 10,000–50,000 documents | M30+ | `m`, `efConstruction` |
+| **DiskANN** | 50,000+ documents | M30+ | `maxDegree`, `lBuild` |
+
+## Prerequisites
+
+- [.NET 8 SDK](https://dotnet.microsoft.com/download/dotnet/8.0)
+- Azure DocumentDB (vCore) cluster
+- Azure OpenAI resource with an embedding model deployed
+- Azure CLI logged in (`az login`) for passwordless authentication
+
+## Setup
+
+1. Copy the environment file and fill in your values:
+
+   ```bash
+   cp .env.example .env
+   ```
+
+2. Edit `.env` with your configuration:
+
+   ```env
+   AZURE_OPENAI_EMBEDDING_MODEL=text-embedding-3-small
+   AZURE_OPENAI_EMBEDDING_ENDPOINT=https://<your-resource>.openai.azure.com
+   MONGO_CLUSTER_NAME=<your-cluster-name>
+   AZURE_DOCUMENTDB_DATABASENAME=Hotels
+   ALGORITHM=all
+   SIMILARITY=COS
+   ```
+
+3. Restore packages:
+
+   ```bash
+   cd src
+   dotnet restore
+   ```
+
+## Usage
+
+Run all algorithms:
+
+```bash
+cd src
+dotnet run
+```
+
+Run a specific algorithm:
+
+```bash
+# Set in .env: ALGORITHM=ivf | hnsw | diskann | all
+dotnet run
+```
+
+## Compare All Algorithms
+
+Run all 9 combinations (3 algorithms × 3 similarity metrics) in a single invocation with a formatted comparison table:
+
+```bash
+# Set in .env: ALGORITHM=compare
+dotnet run
+```
+
+This mode:
+- Uses a **single collection** (`hotels`) with 9 vector indexes
+- Generates **one embedding** for the query, reused across all searches
+- Runs searches **sequentially** with `Stopwatch` timing for fair comparison
+- Prints a formatted table with latency, top result, and scores
+
+**Additional environment variables for compare mode:**
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `QUERY_TEXT` | `luxury hotel near the beach` | Search query text |
+| `TOP_K` | `3` | Number of results per search |
+| `VERBOSE` | `false` | Show detailed per-result output |
+
+**9 Index Combinations:**
+
+| Index Name | Algorithm | Metric | Parameters |
+|------------|-----------|--------|------------|
+| `vector_ivf_cos` | IVF | COS | numLists=1 |
+| `vector_hnsw_cos` | HNSW | COS | m=16, efConstruction=64 |
+| `vector_diskann_cos` | DiskANN | COS | maxDegree=32, lBuild=50 |
+| `vector_ivf_l2` | IVF | L2 | numLists=1 |
+| `vector_hnsw_l2` | HNSW | L2 | m=16, efConstruction=64 |
+| `vector_diskann_l2` | DiskANN | L2 | maxDegree=32, lBuild=50 |
+| `vector_ivf_ip` | IVF | IP | numLists=1 |
+| `vector_hnsw_ip` | HNSW | IP | m=16, efConstruction=64 |
+| `vector_diskann_ip` | DiskANN | IP | maxDegree=32, lBuild=50 |
+
+## Project Structure
+
+```
+select-algorithm-dotnet/
+├── .env.example          # Environment variable template
+├── README.md             # This file
+└── src/
+    ├── SelectAlgorithm.csproj  # Project file
+    ├── Program.cs              # Entry point - dispatches by ALGORITHM env
+    ├── Utils.cs                # Shared helpers (connection, embedding, search)
+    ├── IvfDemo.cs              # IVF index creation and search
+    ├── HnswDemo.cs             # HNSW index creation and search
+    ├── DiskannDemo.cs          # DiskANN index creation and search
+    └── CompareAll.cs           # Unified 9-combination comparison runner
+```
+
+## How It Works
+
+1. **Connect** to DocumentDB using Microsoft Entra ID (OIDC) passwordless authentication
+2. **Load** hotel documents with pre-computed embeddings from `Hotels_Vector.json`
+3. **Create** a vector index using the selected algorithm
+4. **Search** using a natural language query converted to an embedding via Azure OpenAI
+5. **Display** ranked results with similarity scores
+
+## Authentication
+
+This sample uses `DefaultAzureCredential` for both:
+- **DocumentDB**: OIDC-based MongoDB authentication
+- **Azure OpenAI**: Token-based authentication with `https://cognitiveservices.azure.com/.default` scope
+
+Ensure you are logged in with `az login` and have appropriate RBAC roles assigned.