Introduce three new Makefile targets: `create_docs` to merge HTML manual files into a single markdown document using a new wren script, `create_training_data` to generate JSONL training and validation datasets from the manual, and `install` to copy the wren_cli binary to /usr/local/bin.
Add WrenFileReader class in apps/merge_all_wren.wren for recursive .wren file discovery and content printing. Introduce example/strutil_demo.wren demonstrating case conversion, hex encoding, SHA256 hashing, string repetition, padding, HTML/JSON escaping, and URL encoding/decoding. Create manual/api pages for argparse, dataset, html, markdown, uuid, wdantic, and web modules. Update manual/api/index.html sidebar and module count from 21 to 28, adding links and cards for the new modules.
