chore: add Claude Code project context

.claude/commands/validate-compose.md

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+# Validate Docker Compose Stack
+
+Validate the Compose stack named in `$ARGUMENTS`.
+
+If `$ARGUMENTS` is empty, inspect the repository and validate all `*-compose.yml` files you can safely validate.
+
+Steps:
+1. Identify the compose file and matching `.env.example` file.
+2. Run `docker compose config` with the example env file when possible.
+3. Report syntax errors, missing variables, unsupported options, and manual values required.
+4. Do not modify files unless the user asks.