refactor: extract AI/agent files into separate repo

ObsidianDragon-agent/ is now a standalone git repo (future submodule)
so AI configuration files are not pushed to the main repository.

- Remove copilot-instructions.md and ARCHITECTURE.md from main tracking
- Remove symlinks from .github/ and docs/
- Add ObsidianDragon-agent/ and .github/ to .gitignore

.gitignore

@@ -36,6 +36,8 @@ asmap.dat
 /external/xmrig-hac
 /memory
 /todo.md
+/.github/
+/ObsidianDragon-agent/
 
 # macOS
 .DS_Store