Add PII redaction POC for secure LLM prompting.

Implements detect-redact-sanitize pipeline with regex, domain rules, and ONNX NER before the LLM boundary, plus NUnit tests and Xenovex push documentation.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/git-xenovex-setup.md

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+# Git setup — Xenovex (xts.xenovex.com)
+
+This repository is ready for push to your Xenovex Git server after you create a remote repository.
+
+## Prerequisites
+
+- Git 2.x (installed at `C:\Program Files\Git\bin\git.exe`)
+- Access to https://xts.xenovex.com/explore/repos
+- .NET 10 SDK for build/test
+
+## 1. Create the remote repository
+
+1. Sign in to **https://xts.xenovex.com**
+2. Open **Explore repos** (or **New repository**)
+3. Create a new empty repository, e.g. `llm-pii-poc`
+4. Copy the **HTTPS** or **SSH** clone URL (example shapes):
+   - `https://xts.xenovex.com/<org-or-user>/llm-pii-poc.git`
+   - `git@xts.xenovex.com:<org-or-user>/llm-pii-poc.git`
+
+Do **not** initialize the remote with a README if you are pushing an existing local history.
+
+## 2. Add remote and push (from repository root)
+
+```powershell
+cd C:\Users\bilal.n\Projects\llm-pii-poc
+
+# Use full path if git is not on PATH
+$git = "C:\Program Files\Git\bin\git.exe"
+
+& $git remote add origin <YOUR_CLONE_URL>
+& $git branch -M main
+& $git push -u origin main
+```
+
+If the remote already has commits (e.g. auto-generated README), either use an empty remote or:
+
+```powershell
+& $git pull origin main --rebase
+& $git push -u origin main
+```
+
+## 3. What is committed vs excluded
+
+| Included | Excluded (`.gitignore`) |
+|----------|-------------------------|
+| Source (`src/`), tests, scripts, docs | `bin/`, `obj/`, `.vs/` |
+| `README.md`, `PiiRedaction.slnx` | `models/*.onnx`, `vocab.txt`, `ner-labels.txt` (~431MB model) |
+| `models/.gitkeep` (empty models folder) | `scratch/` |
+
+After clone, download the NER model locally:
+
+```powershell
+.\scripts\download-ner-model.ps1
+```
+
+## 4. Verify after clone
+
+```powershell
+dotnet build
+dotnet test
+dotnet run --project src/PiiRedaction.ConsoleApp -- --sample 0
+```