refactor: restructure docs as submodule, add dev-docs/ and AGENTS.md

- Move ASPICE docs to chanoraapp/docs submodule at docs/
- Move development docs to dev-docs/ (superpowers, offline-knowledge, impl-mapping)
- Add AGENTS.md with project conventions for AI agents
- Add impl-mapping.md (SAD component → source file mapping)
- Archive completed plans to dev-docs/superpowers/plans/_archived/
- Remove AGENTS.md from .gitignore (now tracked)

.gitignore

@@ -125,7 +125,6 @@ opencode.json
 /apps/chanora_flutter/macos/Frameworks/
 .opencode/
 .omo/
-AGENTS.md
 Screenshot 2026-05-17 at 22.23.07.png
 
 # Xcode archive / export bundles (generated by Product > Archive > Distribute)