docs(agents): add AGENTS.md context files for all modules

Adds directory-specific agent context templates for AI-assisted
development across all apps and packages.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/coordinator/AGENTS.md

@@ -0,0 +1,18 @@
+# coordinator — Agent Context
+
+> Part of the apps layer.
+
+## Patterns
+
+<!-- Add module-specific patterns as you discover them -->
+
+## Gotchas
+
+<!-- Add things that trip up agents in this module -->
+
+## Key Files
+
+| File | Purpose |
+| ---- | ------- |
+
+<!-- Add important files in this directory -->