Update README for admin HTTP API, mark tasks completed

- Replace admin socket section with admin HTTP API section
- Update config table (admin_socket_path → admin_key_path)
- Update project structure (admin/auth.rs, handler.rs, config/mod.rs)
- Update architecture diagram (Admin HTTP API instead of Unix socket)
- Update Docker compose volume (admin-key instead of socket dir)
- Mark all four task files as status: completed with summaries

tasks/fix/agents-md-project-structure.md

@@ -1,7 +1,7 @@
 ---
 id: fix/agents-md-project-structure
 name: Update AGENTS.md project structure and common modifications after admin refactor
-status: pending
+status: completed
 depends_on: [fix/admin-http-api]
 scope: narrow
 risk: low
@@ -77,4 +77,9 @@ Unix socket (tokio::net::UnixStream).
 
 ## Summary
 
-> To be filled on completion
+Updated project structure (admin/auth.rs, handler.rs, mod.rs; config/mod.rs),
+architecture concepts (admin HTTP API, TOCTOU check, wildcard bind consistency),
+config format (admin_key_path), testing (HTTP-based admin tests), and common
+modifications (curl commands replacing socat). Updated README.md with same
+changes: admin HTTP API section, project structure, architecture diagram, config
+table, and Docker compose volumes.