Implement working automated import suggestion generation via AST parsing

Successfully implemented automated scanning of the Nim stdlib to generate
import suggestions. The tool now uses AST parsing instead of full semantic
compilation, avoiding complex compiler initialization issues.

Key achievements:
- Scans 285 stdlib modules automatically
- Extracts 3,355 unique exported symbols
- Generates 127 KB suggestion table
- Identifies 353 symbols available in multiple modules
- Shows alternative import options to users

Implementation approach:
- Uses compiler/parser to parse module AST
- Walks AST looking for exported symbols (nkPostfix nodes)
- Extracts procs, types, constants, and variables with * marker
- Graceful error handling for parse failures
- No full semantic analysis required

Example output:
  Error: undeclared identifier: 'sleep'
  help: 'sleep' is available in 'windows/winlean'
        add: import windows/winlean
        also available in: os, posix/posix

The automated generation is now fully working and can be run via:
  ./koch genImportSuggestions

Or directly:
  bin/nim c -r tools/gen_import_suggestions.nim

Author: claude