fix: show actual memory usage (exclude cache) + add build:container script

- Dashboard memory: use /proc/meminfo MemAvailable instead of os.freemem()
  to exclude Linux buffer/cache from reported usage
- Add build:container npm script for reviewer Docker image rebuild
- Update deploy commands in CLAUDE.md and README.md to include build:container

CLAUDE.md

@@ -40,6 +40,7 @@ Run commands directly—don't tell the user to run them.
 ```bash
 bun run build                              # Build main project
 bun run build:runners                      # Install + build both runners
+bun run build:container                    # Rebuild reviewer Docker image
 bun run dev                                # Dev mode with hot reload
 ```
 
@@ -52,7 +53,7 @@ journalctl --user -u ejclaw -f                    # Follow logs
 
 Deploy to server (build on server, not locally):
 ```bash
-ssh clone-ej@100.64.185.108 'cd ~/EJClaw && git pull && bun run build && bun run build:runners && systemctl --user restart ejclaw'
+ssh clone-ej@100.64.185.108 'cd ~/EJClaw && git pull && bun run build && bun run build:runners && bun run build:container && systemctl --user restart ejclaw'
 ```
 
 ## Service Stack Architecture