Add narrative-first Copilot scaffolding and staged skill intake for Sprint 0

[Copilot]

This change prepares the repo for AI-assisted story development before mechanika/ is finalized. It makes the recommended design/documentation skills usable locally now, and adds a controlled place to stage additional skills before promoting them into the active workflow.

• Narrative-first workflow

  • Added new prompts for:
    • /game-brief
    • /fabula
    • /gdd
    • /investigate
  • Established the intended Sprint 0 order:
    • /game-dev → /game-brief → /fabula → /gdd → /skills-adoption

• Local skill availability

  • Added repo-local skills for:
    • mechanika-spec
    • story-bible
    • skill-creator
    • content-research-writer
  • Kept these aligned with existing repo rules: no premature gameplay logic, no mechanika invention, docs-first adoption.

• Skill intake/staging

  • Added .github/skills/incoming/ as the staging area for uploaded/imported skills.
  • Documented the promotion path from draft skill → adapted local skill → workflow/docs exposure.

• Durable story/design docs

  • Added:
    • docs/GAME_BRIEF.md
    • docs/FABULA.md
    • docs/GDD.md
  • Separated story canon from gameplay rules:
    • docs/FABULA.md for narrative/worldbuilding
    • mechanika/ for gameplay mechanics/spec

• Workflow and documentation updates

  • Updated README.md, docs/COPILOT_WORKFLOW.md, docs/ARCHITECTURE.md, .github/copilot-instructions.md, docs/skills-adoption/README.md, and SKILLS_RECOMMENDATIONS.txt
  • Exposed the new prompts/skills in the documented workflow and marked narrative/story work as an explicit pre-mechanika phase

Example of the new intended flow:

/game-dev sprawdź stan projektu i podaj następne 1-3 kroki
/game-brief uporządkuj krótki brief projektu i misji
/fabula przygotuj bazę fabularną, ton i haki narracyjne do docs/FABULA.md
/gdd zsynchronizuj brief, fabułę i aktualny scope