docs(impact): condense to one-page statement, keep long version as -FULL

The WoT-a-thon brief asks for a "one-page impact statement". The
existing IMPACT-STATEMENT.md was 317 lines — comprehensive but
unreadable in one sitting.

- IMPACT-STATEMENT.md → 71-line one-pager: problem, solution,
  differentiation, key metrics, NIP-85 compliance, business model,
  3 reasons to win. Drops the mermaid diagram, JSON examples,
  per-audience sections, the post-hackathon roadmap, and the
  technology stack list.
- IMPACT-STATEMENT-FULL.md → unchanged copy of the original 317-line
  long version, kept as the deep-dive companion.

Numbers updated to reflect actual prod yield: 66 strict NIP-85 events
(65 mined + 1 self-declaration) and 466 tests (verified via vitest).

Author: proofoftrust21