CLI: interactive add-source wizard

[vnmoorthy]

reweave add <url> --golden file.json works but writing the JSON by hand is friction. A wizard would:

1. fetch the page and show detected repeating text blocks
2. prompt: 'paste 2-3 titles/prices you can see'
3. build the golden list, call surgeon.bootstrap_spec, show the synthesized spec + sample rows, confirm, save

Everything needed exists in reweave/surgeon.py (bootstrap_spec) and reweave/server.py::add_source — this is UI work in cli.py. Good first issue: no core changes required.