Phase 6 (continued): Port AdoInspectorService + ado2gh generate-script command

- Port AdoInspectorService to pkg/ado/inspector.go with caching, org/project/repo/pipeline discovery, PR counts, CSV loading, and ReplaceInvalidCharactersWithDash
- Port ado2gh generate-script command with all 17 flags, sequential and parallel script generation modes
- Three-level iteration (orgs → team projects → repos) with conditional team creation, service connection sharing, pipeline rewiring
- Two-phase parallel script: queue phase with ExecAndGetMigrationID + wait/post-migration phase with ExecBatch
- Add ExecBatchFunctionBlock and ValidateADOEnvVars to pkg/scriptgen/templates.go
- Wire generate-script into cmd/ado2gh/main.go
- 20+ inspector tests, 28 generate-script tests, all passing
- 0 lint issues in ado packages

Author: offbyone