docs: add comprehensive architecture documentation and Windows development guide

[cbnsndwch]

PR Description

Summary

This PR improves the project's documentation by adding detailed architecture explanations, module references, and a dedicated Windows development setup guide (because that's where I'm developing with it 😄).

Motivation

The existing README was minimal and didn't explain the project's architecture or how the components work together. This makes it difficult for new contributors to understand the codebase and for potential users to evaluate whether DDP Router fits their needs.

Changes

New: DEVELOPING.md

Added a comprehensive guide for building on Windows (msvc):

• Documents the required Rust version (1.79.0) to avoid dependency build errors with newer toolchains
• Provides step-by-step instructions for installing the minimal toolchain profile
• Includes commands for setting up project-specific Rust version overrides
• Shows both debug and release build commands with expected output

Expanded: README.md

Completely restructured and expanded the README with:

• Table of Contents for easy navigation
• Architecture diagram showing the component relationships (Session Manager → Mergebox → Subscriptions → Watcher → MongoDB)
• Core Concepts section explaining DDP, Mergebox, Cursors, and the Watcher
• "Can I Use This Outside Meteor?" section with:
  • Feasibility matrix for different use cases
  • List of standalone-capable modules
  • Code example for building a non-Meteor system
• Module Reference documenting every source file's purpose
• Supported Query Features tables showing operator and cursor option support
• Improved Quick Start with clearer step-by-step instructions
• Sequence diagrams for subscription flow and fallback behavior
• Limitations table with workarounds

Modified: .gitignore

Excluded /.local, /.github, and /.vscode from git index

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

This PR significantly enhances the documentation for the DDP Router project by adding comprehensive architecture explanations, detailed module references, and platform-specific development guidance.

Changes:

• Added extensive architecture documentation to README.md including diagrams, core concepts, module references, and feature support matrices
• Created DEVELOPING.md with Windows-specific build instructions and Rust version requirements
• Added VS Code workspace settings for spell-checking technical terms

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
README.md	Completely restructured with architecture diagrams, core concepts, module reference, supported features tables, and expanded quick start guide
DEVELOPING.md	New Windows development guide with Rust 1.79.0 installation instructions and build commands
.vscode/settings.json	VS Code spell-checker configuration for project-specific technical terms

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