chore: track .claude/rules/ and add self-maintenance instruction

Un-ignore .claude/rules/ so path-scoped rule files are shared via git.
Add instruction in CLAUDE.md to update rule files when modifying classes,
controllers, endpoints, or metrics — keeps rules current as part of
normal workflow rather than requiring separate maintenance.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -67,6 +67,10 @@ PostgreSQL (Flyway): `cameleer-server-app/src/main/resources/db/migration/`
 
 ClickHouse: `cameleer-server-app/src/main/resources/clickhouse/init.sql` (run idempotently on startup)
 
+## Maintaining .claude/rules/
+
+When adding, removing, or renaming classes, controllers, endpoints, UI components, or metrics, update the corresponding `.claude/rules/` file as part of the same change. The rule files are the class/API map that future sessions rely on — stale rules cause wrong assumptions. Treat rule file updates like updating an import: part of the change, not a separate task.
+
 ## Disabled Skills
 
 - Do NOT use any `gsd:*` skills in this project. This includes all `/gsd:` prefixed commands.