docs: update documentation for v2.3.2 and remove legacy files

Major documentation cleanup and updates:

Updates:
- Add USE_FIXED_HTTP=true to all Docker and HTTP deployment examples
- Update main README with v2.3.2 release notes and version badges
- Add HTTP server troubleshooting section for stream errors
- Update CHANGELOG with v2.3.1 and v2.3.2 entries
- Update all configuration examples (.env.example, docker-compose.yml)
- Add clear instructions for using the fixed HTTP implementation

Removed legacy documentation (11 files):
- Implementation plans that have been completed
- Architecture analysis documents
- Intermediate fix documentation
- Planning documents for features now implemented
- Duplicate SETUP.md (content merged into INSTALLATION.md)

The documentation now accurately reflects the current v2.3.2 state
with the complete HTTP server fix using USE_FIXED_HTTP=true.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/INSTALLATION.md

@@ -16,7 +16,10 @@ The fastest way to get n8n-MCP running:
 
 ```bash
 # Using Docker (recommended)
-echo "AUTH_TOKEN=$(openssl rand -base64 32)" > .env
+cat > .env << EOF
+AUTH_TOKEN=$(openssl rand -base64 32)
+USE_FIXED_HTTP=true
+EOF
 docker compose up -d
 ```
 
@@ -46,6 +49,7 @@ docker compose up -d
        
        environment:
          MCP_MODE: ${MCP_MODE:-http}
+         USE_FIXED_HTTP: ${USE_FIXED_HTTP:-true}
          AUTH_TOKEN: ${AUTH_TOKEN:?AUTH_TOKEN is required}
          NODE_ENV: ${NODE_ENV:-production}
          LOG_LEVEL: ${LOG_LEVEL:-info}