test: add unit tests for webappDiscovery and command not found errors

- Add comprehensive tests for webappDiscovery.ts (39 tests)
  - findWebapplicationsFolder: case-insensitive, upward/downward traversal
  - findAllWebapps: discovery with/without manifest, sorting, currentWebappName
  - findWebappByName: lookup by name or manifest name
  - discoverWebapp: selection priority (--name, auto-select, single, multiple)
  - formatWebappChoices: display formatting for selection prompt
- Add tests for "command not found" error detection in DevServerErrorParser

Author: deepu-mungamuri94