v1.13 — Upgrades without collisions

From the same field report: upgrading a derived project meant guessing its base, renumbering the
template's ADRs around the project's own, and losing local script extensions to "copy".

• .anew-version records the ANEW version a workspace is based on; scripts/doctor prints it
  (ok ANEW base version: v1.13) and warns when it is missing. In the template, scripts/selftest
  checks it matches the newest CHANGELOG entry.
• The template's decisions move to docs/decisions/anew/ as ANEW-0001 … ANEW-0009 (each
  with a Revised: line; decisions unchanged), plus ANEW-0010 recording why. Project ADRs number
  from 0001 in docs/decisions/ with no collisions; prompts/adr.md counts only those.
• CHANGELOG opens with "How to upgrade": base from .anew-version, behavior lists for scripts,
  one-line intents for documents, a diff link per release.
• scripts/selftest checks usage output by its usage: prefix and exit code, not its full text,
  so a legitimate extension of a script's arguments is not reported as a difference.

Upgrading

• .anew-version (new): one line, v1.13.
• scripts/doctor (behavior): print ANEW base version: <first line of .anew-version> as ok;
  warn when the file is missing. Never fail on it.
• scripts/selftest (behavior): usage assertions match usage: only; fixture copies
  .anew-version; the version scenarios above.
• docs/decisions/: move the template decisions you have (ADR 0001–0009 as shipped by ANEW, if
  you kept them in your own range) to docs/decisions/anew/ under their ANEW-NNNN names, or take
  the folder from v1.13 and delete your copies. Your own ADRs stay where they are; one that had
  to be renumbered around a template ADR may keep its number. Add ANEW-0010.
• docs/decisions/README.md: intent — two owners, two places; the next project number counts
  only docs/decisions/.
• prompts/adr.md: intent — NNNN is the highest in docs/decisions/ + 1, anew/ excluded.
• README: the docs/decisions/ row names the two places.
• Full diff: v1.12...v1.13