fix(rules-injector): respect claude_code config for user rule loading

When claude_code integration is disabled in oh-my-opencode.json, the
rules-injector now skips loading rules from ~/.claude/rules/ to prevent
Claude Code-specific instructions from leaking into non-Claude agents
(e.g., GPT-5.4 Sisyphus), which causes agent hallucination.

Also adds ~/.sisyphus/rules/ and ~/.opencode/rules/ as OpenCode-native
user rule directories that are always searched regardless of config.

Fixes #2920

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