feat(bloblang): Improve Bloblang playground with Go/WASM migration

[iamramtin]

Summary

Improves the Bloblang playground by migrating core logic from JavaScript to Go/WASM.

The playground previously duplicated some of Bloblang logic in JavaScript, creating maintenance overhead and potential inconsistencies. By moving to Go/WASM, we:

• Better align it with the rest of the codebase
• Reuse existing Bloblang environment and validation logic directly
• Eliminate duplication between Go and JS implementations
• Improve type safety and error handling
• Maintain a closer source of truth for Bloblang behavior

Changes

Go/WASM Migration:

• Migrated execution, validation, formatting, autocompletion, and other utilities from JS to Go/WASM
• Split blobl package into focused modules (core, editor, server, wasm, types)
• Simplified WASM initialization and auto-register server/WASM handlers
• Added elementary test suite for core playground functions (verifies playground-specific behavior without duplicating existing Bloblang tests)

JavaScript Simplification:

• Extracted BloblangAPI abstraction layer for WASM/server routing
• Removed unused code, dead methods, redundant functionality
• Improved error handling and WASM initialization flow

Other Improvements:

• Improved autocomplete with pre-rendered HTML docs and smarter context detection
• Replaced hardcoded values with CSS variables and duplicate rules
• Improved mobile responsive layout and overall UX

Testing

1. Run Unit Tests

make playground-test

2. Test Server Mode (Go backend via HTTP)

# Build and run playground server
go build -o bento ./cmd/bento/main.go
make playground
./bento blobl playground -p 3001 --no-open

Visit playground and verify:

• Playground loads without errors
• Execute mappings (try: root.name = this.name.uppercase())
• Format mappings (Cmd/Ctrl+Shift+F or Format button)
• Autocomplete works (type root = and trigger autocomplete)
• Error messages display correctly for invalid input/mappings
• Theme toggle works (light/dark mode)

3. Test WASM Mode (Client-side execution)

# Clean and rebuild
rm -rf website/static/playground
make docs
make playground
cd website && yarn start

Visit the playground in the docs and verify:

• Playground loads in iframe without errors
• All functionality from server mode works (execution, formatting, autocomplete)
• Theme syncs with Docusaurus theme
• Responsive layout works on mobile viewport (resize browser)
• Full-screen mode works (click "Open in Full Screen" button)

Breaking Changes

None