feat: make --name flag optional with intelligent webapp discovery

- Add webappDiscovery.ts for recursive webapp.json file discovery
- Make --name flag optional in sf webapp dev command
- Auto-select when single webapp.json found
- Prompt user to select when multiple webapp.json files found
- Search excludes node_modules, .git, dist, build, out, coverage
- Update documentation with discovery flow diagram
- Update messages for new discovery scenarios

Author: deepu-mungamuri94