Add 18 new prompts files (#56)

* Add prompts for .NET best practices, design pattern review, and GitHub Copilot suggestions

- Introduced a comprehensive prompt for ensuring .NET/C# code adheres to best practices, covering documentation, design patterns, dependency injection, resource management, async patterns, testing standards, configuration, AI integration, error handling, performance, security, and code quality.
- Added a prompt for reviewing C#/.NET code for design pattern implementation, providing a checklist for required patterns, architecture, best practices, SOLID principles, performance, maintainability, testability, security, documentation, code clarity, and clean code.
- Created prompts for suggesting relevant GitHub Copilot chatmodes and prompts based on the current repository context, including a structured process for fetching available chatmodes/prompts, scanning local files, and presenting options with rationale.
- Developed a prompt for updating Azure Verified Modules (AVM) in Bicep files, detailing the process for scanning, checking for updates, validating, and handling breaking changes.
- Implemented a prompt for updating implementation plans with new requirements, ensuring machine-readable output and adherence to a strict template.
- Added a prompt for updating the llms.txt file to reflect changes in documentation or specifications, focusing on compliance with the llmstxt specification.
- Created a prompt for updating markdown file indices with files from specified folders, including options for table structures and update strategies.
- Developed a prompt for updating object-oriented component documentation, following industry best practices and ensuring alignment with current implementations.
- Added a prompt for updating specification files, emphasizing clarity, structure, and compliance with established documentation standards.

* CHANGE: Update implementation plan prompt formatting

- Renamed prompt title for clarity.
- Added spacing for improved readability.
- Enhanced structure to ensure compliance with template validation rules.

* CHANGE: Fix typo in .NET best practices prompt

- Corrected "soltion" to "solution" in the prompt description.

prompts/update-markdown-file-index.prompt.md

@@ -0,0 +1,76 @@
+---
+mode: 'agent'
+description: 'Update a markdown file section with an index/table of files from a specified folder.'
+tools: ['changes', 'codebase', 'editFiles', 'extensions', 'fetch', 'findTestFiles', 'githubRepo', 'openSimpleBrowser', 'problems', 'runCommands', 'runTasks', 'runTests', 'search', 'searchResults', 'terminalLastCommand', 'terminalSelection', 'testFailure', 'usages', 'vscodeAPI']
+---
+# Update Markdown File Index
+
+Update markdown file `${file}` with an index/table of files from folder `${input:folder}`.
+
+## Process
+
+1. **Scan**: Read the target markdown file `${file}` to understand existing structure
+2. **Discover**: List all files in the specified folder `${input:folder}` matching pattern `${input:pattern}`
+3. **Analyze**: Identify if an existing table/index section exists to update, or create new structure
+4. **Structure**: Generate appropriate table/list format based on file types and existing content
+5. **Update**: Replace existing section or add new section with file index
+6. **Validate**: Ensure markdown syntax is valid and formatting is consistent
+
+## File Analysis
+
+For each discovered file, extract:
+
+- **Name**: Filename with or without extension based on context
+- **Type**: File extension and category (e.g., `.md`, `.js`, `.py`)
+- **Description**: First line comment, header, or inferred purpose
+- **Size**: File size for reference (optional)
+- **Modified**: Last modified date (optional)
+
+## Table Structure Options
+
+Choose format based on file types and existing content:
+
+### Option 1: Simple List
+
+```markdown
+## Files in ${folder}
+
+- [filename.ext](path/to/filename.ext) - Description
+- [filename2.ext](path/to/filename2.ext) - Description
+```
+
+### Option 2: Detailed Table
+
+| File | Type | Description |
+|------|------|-------------|
+| [filename.ext](path/to/filename.ext) | Extension | Description |
+| [filename2.ext](path/to/filename2.ext) | Extension | Description |
+
+### Option 3: Categorized Sections
+
+Group files by type/category with separate sections or sub-tables.
+
+## Update Strategy
+
+- 🔄 **Update existing**: If table/index section exists, replace content while preserving structure
+- ➕ **Add new**: If no existing section, create new section using best-fit format
+- 📋 **Preserve**: Maintain existing markdown formatting, heading levels, and document flow
+- 🔗 **Links**: Use relative paths for file links within the repository
+
+## Section Identification
+
+Look for existing sections with these patterns:
+
+- Headings containing: "index", "files", "contents", "directory", "list"
+- Tables with file-related columns
+- Lists with file links
+- HTML comments marking file index sections
+
+## Requirements
+
+- Preserve existing markdown structure and formatting
+- Use relative paths for file links
+- Include file descriptions when available
+- Sort files alphabetically by default
+- Handle special characters in filenames
+- Validate all generated markdown syntax