Add facts-only codebase scan to /sd:setup

[developzoneio]

What

Implements the Planned roadmap item /sd:setup codebase scan. Turns first-run setup from a
blank <<placeholder>> template into detected defaults - facts only, never constitution rules.

Changes

• commands/setup.md - new Phase 2.5 "Scan codebase (facts only)" (Claude-driven bounded
  sampling: stack, paths.{src,tests,docs}, commands.* from the project manifest, and an ordered
  inside-out paths.layers map). Adds a single batch confirmation gate (not a 4th question),
  wires detected facts into Phase 4 (CLAUDE.md) and Phase 6 (project-config.json), and adds a Rules
  bullet pinning the facts-only boundary.
• templates/project-config.template.json - adds paths.layers: [] with a usage note.
• CHANGELOG.md - [Unreleased] -> Added entry.
• docs/superpowers/ - design doc + implementation plan for traceability.

Design decisions

• Facts only - constitution rules stay human-authored; auto-inferring them risks codifying
  accidental patterns as enforced law.
• No scanner script - the scan is prompt-driven sampling inside setup.md, keeping the engine
  stack-agnostic with no cross-platform ps1/sh pair to maintain.
• paths.layers is an ordered inside-out [{name, path}] array - order encodes dependency
  direction, backing constitution 1.1.

Verification

• scripts/validate.ps1 - all 6 checks pass (command count unchanged at 10; [Unreleased] gate
  satisfied).
• Added lines are pure ASCII (pre-existing em-dash/x glyphs untouched; .md not subject to the
  .ps1-only ASCII gate).

Constraints preserved: <=3 interactive questions, idempotent, stack-agnostic, no BOM, engine never
modified.

🤖 Generated with Claude Code