Add llms.txt and CITATION.cff for discoverability (#630)

- llms.txt: structured project summary for LLM crawlers (llmstxt.org standard)
- CITATION.cff: enables GitHub "Cite this repository" widget + structured metadata

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: erikdarlingdata

CITATION.cff

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+cff-version: 1.2.0
+title: "SQL Server Performance Monitor"
+message: "If you use this software, please cite it as below."
+type: software
+authors:
+  - given-names: Erik
+    family-names: Darling
+    affiliation: "Darling Data, LLC"
+    website: "https://erikdarling.com"
+repository-code: "https://github.com/erikdarlingdata/PerformanceMonitor"
+url: "https://erikdarling.com/free-sql-server-performance-monitoring/"
+license: MIT
+version: "2.3.0"
+date-released: "2026-03-18"
+keywords:
+  - sql-server
+  - performance-monitoring
+  - database-monitoring
+  - dba-tools
+  - mcp-server
+  - wait-stats
+  - execution-plans

llms.txt

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+# SQL Server Performance Monitor
+
+> Free, open-source SQL Server performance monitoring tool by Erik Darling (Darling Data, LLC). 32 T-SQL collectors, real-time alerts, graphical execution plan viewer, and a built-in MCP server with 51-63 tools for AI-powered analysis. Two editions: Full (server-installed with SQL Agent) and Lite (standalone desktop app with DuckDB storage). Replaces expensive commercial tools like SentryOne and Solarwinds DPA. MIT licensed.
+
+- Supports SQL Server 2016-2025, Azure SQL Managed Instance, AWS RDS for SQL Server, and Azure SQL Database (Lite only)
+- Monitors wait stats, query performance, blocking chains, deadlocks, memory grants, file I/O, tempdb, CPU, perfmon counters, and more
+- Real-time alerts via system tray notifications and styled HTML emails
+- Built-in MCP server exposes monitoring data to Claude Code, Cursor, and other LLM clients
+- 4,300+ downloads across releases
+
+## Documentation
+
+- [README](https://github.com/erikdarlingdata/PerformanceMonitor/blob/main/README.md): Complete documentation including quick start, permissions, collector reference, alert configuration, MCP server setup, and edition comparison
+- [Releases](https://github.com/erikdarlingdata/PerformanceMonitor/releases): Download pre-built binaries
+- [Product page](https://erikdarling.com/free-sql-server-performance-monitoring/): Overview and commercial support options
+
+## Optional
+
+- [Third-party notices](https://github.com/erikdarlingdata/PerformanceMonitor/blob/main/THIRD_PARTY_NOTICES.md): License information for bundled components
+- [License](https://github.com/erikdarlingdata/PerformanceMonitor/blob/main/LICENSE): MIT License