[v2.0] README and SKILL.md positioning — spec layer, not full orchestration

[FredAntB]

Context

The current README implies the skill is a complete SDD solution. Discord
beta feedback correctly identified this as a positioning gap — the skill
is the spec generation layer, not a full workflow orchestration framework.
Clarifying this turns a perceived weakness into a composability feature.

Goal

README and SKILL.md should clearly position the skill as the spec layer
in a larger AI development stack, composable with GSD, BMAD, Superpowers,
and similar frameworks.

Proposed work

README changes

• Add ## Works with section listing GSD, BMAD, Superpowers with
  one-line descriptions of how each complements this skill
• Update the opening paragraph to include: "Designed to be the spec
  layer in a larger AI development stack"
• Add a composability diagram:
  spec-driven-development → execution framework → review layer

SKILL.md changes

• Add a ## Scope section at the top making explicit what the skill
  does and does not cover
• Does: spec generation, cross-AI config, session continuity, retrofit
• Does not: execution orchestration, subagent management,
  parallelization, code review, token optimization

Teaching content

• Add Level 5+ to sdd-curriculum.md covering how SDD integrates with
  execution frameworks for larger projects

Success condition

A developer arriving from GSD or BMAD immediately understands how this
skill fits into their existing workflow rather than seeing it as a competitor.

References

• GSD: https://github.com/taches-app/gsd
• BMAD: https://github.com/bmad-method
• Superpowers: community framework
• Discord feedback thread (beta issue [beta-friction] Discord feedback — skill scope vs full workflow orchestration #5 )