Alpha CLI

Initialize PathDigest project with core functionality and dependencies

- Added `go.mod` and `go.sum` for dependency management.
- Implemented main command structure in `cmd/root.go` using Cobra.
- Created `README.md` with project description and usage instructions.
- Developed core ingestion logic in `internal/digest/ingest.go` to process Git repositories and local directories.
- Introduced file handling utilities in `internal/fsutil/fs.go`.
- Added Git utilities for repository management in `internal/gitutil/git.go`.
- Established default exclusion patterns for file processing in `internal/digest/defaults.go`.
- Implemented output formatting in `internal/digest/format.go`.
- Added tests for path matching functionality in `internal/digest/ingest_test.go`.
- Defined data structures for ingestion options and results in `internal/digest/types.go`.
- Created a main entry point in `cmd/pathdigest/main.go` to execute the application.