feat: Add cryptofind CLI and core scanner functionality

Co-authored-by: script3r <[email protected]>

Author: cursoragent

CONTRIBUTING.md

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+## Contributing to cryptofind
+
+Thank you for improving cryptofind! This project aims for speed, precision, and extensibility.
+
+### Adding a New Library via patterns
+
+1. Edit `patterns.toml` and add a new `[[library]]` entry.
+2. Use anchored regexes for `include`/`import`/`namespace`/`apis`.
+3. Prefer import/include anchors; use API patterns only as secondary evidence.
+4. Run `cargo test` to validate regex and stripper behavior.
+
+### Adding a New Language or Custom Detector
+
+1. Create a new crate under `crates/detector-<lang>/`.
+2. Implement the `Detector` trait from `scanner-core`.
+3. Provide `prefilter()` substrings and extensions for fast filtering.
+4. Use comment stripping utilities to avoid matches in comments/strings.
+
+### Performance Guidelines
+
+- Stream files and avoid unnecessary allocations.
+- Use `rayon` for parallelism; keep per-file work independent.
+- Prefer `aho-corasick` for prefilter substring matching.
+- Short-circuit after sufficient evidence unless `--exhaustive` (future work).
+
+### Testing
+
+- Add unit tests for any new stripper rules.
+- Provide fixtures under `fixtures/<lang>/positive` and `fixtures/<lang>/negative`.
+- Add integration tests in `tests/` to cover the new patterns.
+