Publish the BReg-to-Evidence tutorials on evidencectl source add

Found in the 0.28.0 pre-release review (2026-09-08). Line references are as of main after #926.

`tutorials/deploy-evidence-from-breg.mdx` and `tutorials/evidence-from-breg.mdx` are `draft: true`. With 0.28.0 the documented local connection path is `evidencectl source add --project ` (preview, then `--apply`, bregctl of the same version on PATH). Rebase both tutorials on it, verify them against 0.28.0 binaries, and un-draft.

Also add the `source` and `target` command families to `reference/evidencectl.mdx`, which was last reviewed 2026-08-06 and predates both.

Start with tutorials/deploy-evidence-from-breg.mdx and tutorials/evidence-from-breg.mdx, then review reference/evidencectl.mdx and the 0.28.0 evidencectl and bregctl binaries. Rebase both tutorials on the documented source-add flow, verify them against 0.28.0, remove their draft status, and document the source and target command families in the reference page.

Written by the indexing model from the issue text.