Move the three superseded arts design-phase records into the E3 corpus
(already indexed in docs/decisions.md), verbatim-as-historical:
- docs/decisions/design-connection.md (from src/arts/connection/DESIGN_CONN.md)
- docs/decisions/design-session.md (from src/arts/session/DESIGN.md)
- docs/decisions/design-timer.md (from src/arts/timer/DESIGN_TIMR.md, kept Spanish)
Each gets a `status: historical` frontmatter block; the current reference for
each subsystem is its README.md. A stub at every old src/arts/* path keeps the
~30 source provenance citations (`DESIGN_TIMR §12.8`, `DESIGN.md §7.Q1`, …)
resolving. Bodies kept verbatim (no reformat). docs/decisions.md index + naming
note updated to the new paths. docs:check 0 errors.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
